目录

简介

字段out,autoFlush,trouble,formatter,psOut,lineSeparator，toCharset方法

9个构造函数

方法ensureOpen,flush,close,checkError,setError,clearError

5个write方法，newLine方法

9个print方法

10个println方法

2个printf方法，2个format方法，3个append方法

简介

package java.io;

import java.util.Objects;
import java.util.Formatter;
import java.util.Locale;
import java.nio.charset.Charset;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException;

/**
 * 将对象的格式化表示形式打印到文本输出流。
 * 这个类实现了在PrintStream中找到的所有打印方法。
 * 它不包含写原始字节的方法，因为程序应该使用未编码的字节流。
 *
 * <p> 与PrintStream类不同的是，如果启用了自动刷新，
 * 那么自动刷新只会在调用println、printf或format方法之一时进行，而不是在输出换行符时进行。
 * 这些方法使用平台自己的line separator概念，而不是换行符。
 *
 * <p> 这个类中的方法永远不会抛出I/O异常，尽管它的一些构造函数可能会。
 * 客户端可以通过调用checkError()来查询是否有错误发生。
 *
 * @author      Frank Yellin
 * @author      Mark Reinhold
 * @since       JDK1.1
 */

public class PrintWriter extends Writer 

字段out,autoFlush,trouble,formatter,psOut,lineSeparator，toCharset方法

    /**
     * 此PrintWriter的底层字符输出流。
     *
     * @since 1.2
     */
    protected Writer out;

    private final boolean autoFlush;
    private boolean trouble = false;
    private Formatter formatter;
    private PrintStream psOut = null;

    /**
     * 行分隔符字符串。这是创建流时的line.separator值。。
     */
    private final String lineSeparator;

    /**
     * 返回给定字符集名称的Charset对象。
     * @throws NullPointerException          is csn is null
     * @throws UnsupportedEncodingException  if the charset is not supported
     */
    private static Charset toCharset(String csn)
        throws UnsupportedEncodingException
    {
        Objects.requireNonNull(csn, "charsetName");
        try {
            return Charset.forName(csn);
        } catch (IllegalCharsetNameException|UnsupportedCharsetException unused) {
            // UnsupportedEncodingException should be thrown
            throw new UnsupportedEncodingException(csn);
        }
    }

9个构造函数

    /**
     * 创建一个新的PrintWriter，不需要自动刷新行。
     *
     * @param  out        A character-output stream
     */
    public PrintWriter (Writer out) {
        this(out, false);
    }

    /**
     * 创建一个新的PrintWriter。
     *
     * @param  out        A character-output stream
     * @param  autoFlush  A boolean; if true, the <tt>println</tt>,
     *                    <tt>printf</tt>, or <tt>format</tt> methods will
     *                    flush the output buffer
     */
    public PrintWriter(Writer out,
                       boolean autoFlush) {
    	// 以out为lock
        super(out);
        // 赋值out和autoFlush
        this.out = out;
        this.autoFlush = autoFlush;
        // 赋值lineSeparator
        lineSeparator = java.security.AccessController.doPrivileged(
            new sun.security.action.GetPropertyAction("line.separator"));
    }

    /**
     * 从现有的OutputStream创建一个新的PrintWriter，不需要自动刷新行。
     * 这个方便的构造函数创建了必要的中间值OutputStreamWriter，它将使用默认的字符编码将字符转换为字节。
     *
     * @param  out        An output stream
     *
     * @see java.io.OutputStreamWriter#OutputStreamWriter(java.io.OutputStream)
     */
    public PrintWriter(OutputStream out) {
        this(out, false);
    }

    /**
     * 从现有的输出流创建一个新的PrintWriter。
     * 这个方便的构造函数创建了必要的OutputStreamWriter，它将使用默认的字符编码将字符转换为字节。
     *
     * @param  out        An output stream
     * @param  autoFlush  A boolean; if true, the <tt>println</tt>,
     *                    <tt>printf</tt>, or <tt>format</tt> methods will
     *                    flush the output buffer
     *
     * @see java.io.OutputStreamWriter#OutputStreamWriter(java.io.OutputStream)
     */
    public PrintWriter(OutputStream out, boolean autoFlush) {
    	// 通过out创建OutputStreamWriter ，再创建BufferedWriter，再调用PrintWriter(Writer out, boolean autoFlush)
        this(new BufferedWriter(new OutputStreamWriter(out)), autoFlush);

        // 保存打印流错误传播
        if (out instanceof java.io.PrintStream) {
            psOut = (PrintStream) out;
        }
    }

    /**
     * 使用指定的文件名创建一个新的PrintWriter，不需要自动刷新行。
     * 这个方便的构造函数创建了必要的中间值OutputStreamWriter，
     * 它将使用Java虚拟机的这个实例的默认字符集对字符进行编码。
     *
     * @param  fileName
     *         The name of the file to use as the destination of this writer.
     *         If the file exists then it will be truncated to zero size;
     *         otherwise, a new file will be created.  The output will be
     *         written to the file and is buffered.
     *
     * @throws  FileNotFoundException
     *          If the given string does not denote an existing, writable
     *          regular file and a new regular file of that name cannot be
     *          created, or if some other error occurs while opening or
     *          creating the file
     *
     * @throws  SecurityException
     *          If a security manager is present and {@link
     *          SecurityManager#checkWrite checkWrite(fileName)} denies write
     *          access to the file
     *
     * @since  1.5
     */
    public PrintWriter(String fileName) throws FileNotFoundException {
        this(new BufferedWriter(new OutputStreamWriter(new FileOutputStream(fileName))),
             false);
    }

    /* 私有构造器 */
    private PrintWriter(Charset charset, File file)
        throws FileNotFoundException
    {
        this(new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file), charset)),
             false);
    }

    /**
     * 使用指定的文件名和字符集创建一个新的打印程序，不需要自动刷新行。
     * 这个方便的构造函数创建必要的中间OutputStreamWriter，它将使用提供的charset编码字符。
     *
     * @param  fileName
     *         The name of the file to use as the destination of this writer.
     *         If the file exists then it will be truncated to zero size;
     *         otherwise, a new file will be created.  The output will be
     *         written to the file and is buffered.
     *
     * @param  csn
     *         The name of a supported {@linkplain java.nio.charset.Charset
     *         charset}
     *
     * @throws  FileNotFoundException
     *          If the given string does not denote an existing, writable
     *          regular file and a new regular file of that name cannot be
     *          created, or if some other error occurs while opening or
     *          creating the file
     *
     * @throws  SecurityException
     *          If a security manager is present and {@link
     *          SecurityManager#checkWrite checkWrite(fileName)} denies write
     *          access to the file
     *
     * @throws  UnsupportedEncodingException
     *          If the named charset is not supported
     *
     * @since  1.5
     */
    public PrintWriter(String fileName, String csn)
        throws FileNotFoundException, UnsupportedEncodingException
    {
        this(toCharset(csn), new File(fileName));
    }

    /**
     * 使用指定的文件创建一个新的PrintWriter，不需要自动刷新行。
     * 这个方便的构造函数创建了必要的中间值OutputStreamWriter，
     * 它将使用Java虚拟机的这个实例的默认字符集对字符进行编码。
     *
     * @param  file
     *         The file to use as the destination of this writer.  If the file
     *         exists then it will be truncated to zero size; otherwise, a new
     *         file will be created.  The output will be written to the file
     *         and is buffered.
     *
     * @throws  FileNotFoundException
     *          If the given file object does not denote an existing, writable
     *          regular file and a new regular file of that name cannot be
     *          created, or if some other error occurs while opening or
     *          creating the file
     *
     * @throws  SecurityException
     *          If a security manager is present and {@link
     *          SecurityManager#checkWrite checkWrite(file.getPath())}
     *          denies write access to the file
     *
     * @since  1.5
     */
    public PrintWriter(File file) throws FileNotFoundException {
        this(new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file))),
             false);
    }

    /**
     * 使用特定的文件和字符集创建一个新的PrintWriter，不需要自动刷新行。
     * 这个方便的构造函数创建了必要的中间程序OutputStreamWriter，
     * 它将使用p给定的charset对字符进行编码。
     *
     * @param  file
     *         The file to use as the destination of this writer.  If the file
     *         exists then it will be truncated to zero size; otherwise, a new
     *         file will be created.  The output will be written to the file
     *         and is buffered.
     *
     * @param  csn
     *         The name of a supported {@linkplain java.nio.charset.Charset
     *         charset}
     *
     * @throws  FileNotFoundException
     *          If the given file object does not denote an existing, writable
     *          regular file and a new regular file of that name cannot be
     *          created, or if some other error occurs while opening or
     *          creating the file
     *
     * @throws  SecurityException
     *          If a security manager is present and {@link
     *          SecurityManager#checkWrite checkWrite(file.getPath())}
     *          denies write access to the file
     *
     * @throws  UnsupportedEncodingException
     *          If the named charset is not supported
     *
     * @since  1.5
     */
    public PrintWriter(File file, String csn)
        throws FileNotFoundException, UnsupportedEncodingException
    {
        this(toCharset(csn), file);
    }

方法ensureOpen,flush,close,checkError,setError,clearError

    /** 检查以确保流没有被关闭 */
    private void ensureOpen() throws IOException {
        if (out == null)
            throw new IOException("Stream closed");
    }

    /**
     * 刷新流。
     * @see #checkError()
     */
    public void flush() {
        try {
            synchronized (lock) {
                ensureOpen();
                // 刷新底层writer out
                out.flush();
            }
        }
        catch (IOException x) {
            trouble = true;
        }
    }

    /**
     * 关闭流并释放与之关联的任何系统资源。关闭先前关闭的流没有效果。
     *
     * @see #checkError()
     */
    public void close() {
        try {
            synchronized (lock) {
                if (out == null)
                    return;
                out.close();
                out = null;
            }
        }
        catch (IOException x) {
            trouble = true;
        }
    }

    /**
     * 如果流未关闭，则刷新流并检查其错误状态。
     *
     * @return <code>true</code> if the print stream has encountered an error,
     *          either on the underlying output stream or during a format
     *          conversion.
     */
    public boolean checkError() {
        if (out != null) {
            flush();
        }
        if (out instanceof java.io.PrintWriter) {
            PrintWriter pw = (PrintWriter) out;
            return pw.checkError();
        } else if (psOut != null) {
            return psOut.checkError();
        }
        // 返回trouble
        return trouble;
    }

    /**
     * 指示发生了错误。
     *
     * <p> 这个方法将导致随后对checkError()的调用返回true，直到调用clearError()。
     */
    protected void setError() {
        trouble = true;
    }

    /**
     * 清除此流的内部错误状态。
     *
     * <p> 此方法将导致后续对checkError()的调用返回false，直到另一个写操作失败并调用setError()。
     *
     * @since 1.6
     */
    protected void clearError() {
        trouble = false;
    }

5个write方法，newLine方法

    /*
     * 异常捕获、同步输出操作，也实现Writer的write()方法
     */

    /**
     * 写入单个字符
     * @param c int specifying a character to be written.
     */
    public void write(int c) {
        try {
            synchronized (lock) {
                ensureOpen();
                // out写入一个字符c
                out.write(c);
            }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }

    /**
     * 写入字符数组的一部分。
     * @param buf Array of characters
     * @param off Offset from which to start writing characters
     * @param len Number of characters to write
     */
    public void write(char buf[], int off, int len) {
        try {
            synchronized (lock) {
                ensureOpen();
                // out写入字符数组buf的len长度
                out.write(buf, off, len);
            }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }

    /**
     * Writes an array of characters.  This method cannot be inherited from the
     * Writer class because it must suppress I/O exceptions.
     * @param buf Array of characters to be written
     */
    public void write(char buf[]) {
        write(buf, 0, buf.length);
    }

    /**
     * Writes a portion of a string.
     * @param s A String
     * @param off Offset from which to start writing characters
     * @param len Number of characters to write
     */
    public void write(String s, int off, int len) {
        try {
            synchronized (lock) {
                ensureOpen();
                out.write(s, off, len);
            }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }

    /**
     * Writes a string.  This method cannot be inherited from the Writer class
     * because it must suppress I/O exceptions.
     * @param s String to be written
     */
    public void write(String s) {
        write(s, 0, s.length());
    }

    private void newLine() {
        try {
            synchronized (lock) {
                ensureOpen();
                // out写入lineSeparator
                out.write(lineSeparator);
                if (autoFlush)
                    out.flush();
            }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }

9个print方法

    /* 不终止行的方法 */

    /**
     * 输出一个布尔值。
     * java.lang.String.valueOf(boolean)生成的字符串根据平台的默认字符编码被转换成字节码，
     * 并且这些字节码完全按照write(int)方法的方式被写入。
     *
     * @param      b   The <code>boolean</code> to be printed
     */
    public void print(boolean b) {
    	// 相当于调用write(String)
        write(b ? "true" : "false");
    }

    /**
     * Prints a character.  The character is translated into one or more bytes
     * according to the platform's default character encoding, and these bytes
     * are written in exactly the manner of the <code>{@link
     * #write(int)}</code> method.
     *
     * @param      c   The <code>char</code> to be printed
     */
    public void print(char c) {
        write(c);
    }

    /**
     * Prints an integer.  The string produced by <code>{@link
     * java.lang.String#valueOf(int)}</code> is translated into bytes according
     * to the platform's default character encoding, and these bytes are
     * written in exactly the manner of the <code>{@link #write(int)}</code>
     * method.
     *
     * @param      i   The <code>int</code> to be printed
     * @see        java.lang.Integer#toString(int)
     */
    public void print(int i) {
        write(String.valueOf(i));
    }

    /**
     * Prints a long integer.  The string produced by <code>{@link
     * java.lang.String#valueOf(long)}</code> is translated into bytes
     * according to the platform's default character encoding, and these bytes
     * are written in exactly the manner of the <code>{@link #write(int)}</code>
     * method.
     *
     * @param      l   The <code>long</code> to be printed
     * @see        java.lang.Long#toString(long)
     */
    public void print(long l) {
        write(String.valueOf(l));
    }

    /**
     * Prints a floating-point number.  The string produced by <code>{@link
     * java.lang.String#valueOf(float)}</code> is translated into bytes
     * according to the platform's default character encoding, and these bytes
     * are written in exactly the manner of the <code>{@link #write(int)}</code>
     * method.
     *
     * @param      f   The <code>float</code> to be printed
     * @see        java.lang.Float#toString(float)
     */
    public void print(float f) {
        write(String.valueOf(f));
    }

    /**
     * Prints a double-precision floating-point number.  The string produced by
     * <code>{@link java.lang.String#valueOf(double)}</code> is translated into
     * bytes according to the platform's default character encoding, and these
     * bytes are written in exactly the manner of the <code>{@link
     * #write(int)}</code> method.
     *
     * @param      d   The <code>double</code> to be printed
     * @see        java.lang.Double#toString(double)
     */
    public void print(double d) {
        write(String.valueOf(d));
    }

    /**
     * Prints an array of characters.  The characters are converted into bytes
     * according to the platform's default character encoding, and these bytes
     * are written in exactly the manner of the <code>{@link #write(int)}</code>
     * method.
     *
     * @param      s   The array of chars to be printed
     *
     * @throws  NullPointerException  If <code>s</code> is <code>null</code>
     */
    public void print(char s[]) {
        write(s);
    }

    /**
     * Prints a string.  If the argument is <code>null</code> then the string
     * <code>"null"</code> is printed.  Otherwise, the string's characters are
     * converted into bytes according to the platform's default character
     * encoding, and these bytes are written in exactly the manner of the
     * <code>{@link #write(int)}</code> method.
     *
     * @param      s   The <code>String</code> to be printed
     */
    public void print(String s) {
        if (s == null) {
            s = "null";
        }
        write(s);
    }

    /**
     * Prints an object.  The string produced by the <code>{@link
     * java.lang.String#valueOf(Object)}</code> method is translated into bytes
     * according to the platform's default character encoding, and these bytes
     * are written in exactly the manner of the <code>{@link #write(int)}</code>
     * method.
     *
     * @param      obj   The <code>Object</code> to be printed
     * @see        java.lang.Object#toString()
     */
    public void print(Object obj) {
        write(String.valueOf(obj));
    }

10个println方法

    /* 终止行的方法 */

    /**
     * 通过写入行分隔符字符串终止当前行。
     * 线分隔符字符串由系统属性line.separator定义。
     * 而不一定是单个换行符 ('\n')。
     */
    public void println() {
        newLine();
    }

    /**
     * 输出一个布尔值，然后终止行。
     * 这个方法的行为就像它调用print(boolean)然后调用println()。
     *
     * @param x the <code>boolean</code> value to be printed
     */
    public void println(boolean x) {
        synchronized (lock) {
            print(x);
            println();
        }
    }

    /**
     * Prints a character and then terminates the line.  This method behaves as
     * though it invokes <code>{@link #print(char)}</code> and then <code>{@link
     * #println()}</code>.
     *
     * @param x the <code>char</code> value to be printed
     */
    public void println(char x) {
        synchronized (lock) {
            print(x);
            println();
        }
    }

    /**
     * Prints an integer and then terminates the line.  This method behaves as
     * though it invokes <code>{@link #print(int)}</code> and then <code>{@link
     * #println()}</code>.
     *
     * @param x the <code>int</code> value to be printed
     */
    public void println(int x) {
        synchronized (lock) {
            print(x);
            println();
        }
    }

    /**
     * Prints a long integer and then terminates the line.  This method behaves
     * as though it invokes <code>{@link #print(long)}</code> and then
     * <code>{@link #println()}</code>.
     *
     * @param x the <code>long</code> value to be printed
     */
    public void println(long x) {
        synchronized (lock) {
            print(x);
            println();
        }
    }

    /**
     * Prints a floating-point number and then terminates the line.  This method
     * behaves as though it invokes <code>{@link #print(float)}</code> and then
     * <code>{@link #println()}</code>.
     *
     * @param x the <code>float</code> value to be printed
     */
    public void println(float x) {
        synchronized (lock) {
            print(x);
            println();
        }
    }

    /**
     * Prints a double-precision floating-point number and then terminates the
     * line.  This method behaves as though it invokes <code>{@link
     * #print(double)}</code> and then <code>{@link #println()}</code>.
     *
     * @param x the <code>double</code> value to be printed
     */
    public void println(double x) {
        synchronized (lock) {
            print(x);
            println();
        }
    }

    /**
     * Prints an array of characters and then terminates the line.  This method
     * behaves as though it invokes <code>{@link #print(char[])}</code> and then
     * <code>{@link #println()}</code>.
     *
     * @param x the array of <code>char</code> values to be printed
     */
    public void println(char x[]) {
        synchronized (lock) {
            print(x);
            println();
        }
    }

    /**
     * Prints a String and then terminates the line.  This method behaves as
     * though it invokes <code>{@link #print(String)}</code> and then
     * <code>{@link #println()}</code>.
     *
     * @param x the <code>String</code> value to be printed
     */
    public void println(String x) {
        synchronized (lock) {
            print(x);
            println();
        }
    }

    /**
     * Prints an Object and then terminates the line.  This method calls
     * at first String.valueOf(x) to get the printed object's string value,
     * then behaves as
     * though it invokes <code>{@link #print(String)}</code> and then
     * <code>{@link #println()}</code>.
     *
     * @param x  The <code>Object</code> to be printed.
     */
    public void println(Object x) {
        String s = String.valueOf(x);
        synchronized (lock) {
            print(s);
            println();
        }
    }

2个printf方法，2个format方法，3个append方法

    /**
     * A convenience method to write a formatted string to this writer using
     * the specified format string and arguments.  If automatic flushing is
     * enabled, calls to this method will flush the output buffer.
     *
     * <p> An invocation of this method of the form <tt>out.printf(format,
     * args)</tt> behaves in exactly the same way as the invocation
     *
     * <pre>
     *     out.format(format, args) </pre>
     *
     * @param  format
     *         A format string as described in <a
     *         href="../util/Formatter.html#syntax">Format string syntax</a>.
     *
     * @param  args
     *         Arguments referenced by the format specifiers in the format
     *         string.  If there are more arguments than format specifiers, the
     *         extra arguments are ignored.  The number of arguments is
     *         variable and may be zero.  The maximum number of arguments is
     *         limited by the maximum dimension of a Java array as defined by
     *         <cite>The Java&trade; Virtual Machine Specification</cite>.
     *         The behaviour on a
     *         <tt>null</tt> argument depends on the <a
     *         href="../util/Formatter.html#syntax">conversion</a>.
     *
     * @throws  java.util.IllegalFormatException
     *          If a format string contains an illegal syntax, a format
     *          specifier that is incompatible with the given arguments,
     *          insufficient arguments given the format string, or other
     *          illegal conditions.  For specification of all possible
     *          formatting errors, see the <a
     *          href="../util/Formatter.html#detail">Details</a> section of the
     *          formatter class specification.
     *
     * @throws  NullPointerException
     *          If the <tt>format</tt> is <tt>null</tt>
     *
     * @return  This writer
     *
     * @since  1.5
     */
    public PrintWriter printf(String format, Object ... args) {
        return format(format, args);
    }

    /**
     * A convenience method to write a formatted string to this writer using
     * the specified format string and arguments.  If automatic flushing is
     * enabled, calls to this method will flush the output buffer.
     *
     * <p> An invocation of this method of the form <tt>out.printf(l, format,
     * args)</tt> behaves in exactly the same way as the invocation
     *
     * <pre>
     *     out.format(l, format, args) </pre>
     *
     * @param  l
     *         The {@linkplain java.util.Locale locale} to apply during
     *         formatting.  If <tt>l</tt> is <tt>null</tt> then no localization
     *         is applied.
     *
     * @param  format
     *         A format string as described in <a
     *         href="../util/Formatter.html#syntax">Format string syntax</a>.
     *
     * @param  args
     *         Arguments referenced by the format specifiers in the format
     *         string.  If there are more arguments than format specifiers, the
     *         extra arguments are ignored.  The number of arguments is
     *         variable and may be zero.  The maximum number of arguments is
     *         limited by the maximum dimension of a Java array as defined by
     *         <cite>The Java&trade; Virtual Machine Specification</cite>.
     *         The behaviour on a
     *         <tt>null</tt> argument depends on the <a
     *         href="../util/Formatter.html#syntax">conversion</a>.
     *
     * @throws  java.util.IllegalFormatException
     *          If a format string contains an illegal syntax, a format
     *          specifier that is incompatible with the given arguments,
     *          insufficient arguments given the format string, or other
     *          illegal conditions.  For specification of all possible
     *          formatting errors, see the <a
     *          href="../util/Formatter.html#detail">Details</a> section of the
     *          formatter class specification.
     *
     * @throws  NullPointerException
     *          If the <tt>format</tt> is <tt>null</tt>
     *
     * @return  This writer
     *
     * @since  1.5
     */
    public PrintWriter printf(Locale l, String format, Object ... args) {
        return format(l, format, args);
    }

    /**
     * Writes a formatted string to this writer using the specified format
     * string and arguments.  If automatic flushing is enabled, calls to this
     * method will flush the output buffer.
     *
     * <p> The locale always used is the one returned by {@link
     * java.util.Locale#getDefault() Locale.getDefault()}, regardless of any
     * previous invocations of other formatting methods on this object.
     *
     * @param  format
     *         A format string as described in <a
     *         href="../util/Formatter.html#syntax">Format string syntax</a>.
     *
     * @param  args
     *         Arguments referenced by the format specifiers in the format
     *         string.  If there are more arguments than format specifiers, the
     *         extra arguments are ignored.  The number of arguments is
     *         variable and may be zero.  The maximum number of arguments is
     *         limited by the maximum dimension of a Java array as defined by
     *         <cite>The Java&trade; Virtual Machine Specification</cite>.
     *         The behaviour on a
     *         <tt>null</tt> argument depends on the <a
     *         href="../util/Formatter.html#syntax">conversion</a>.
     *
     * @throws  java.util.IllegalFormatException
     *          If a format string contains an illegal syntax, a format
     *          specifier that is incompatible with the given arguments,
     *          insufficient arguments given the format string, or other
     *          illegal conditions.  For specification of all possible
     *          formatting errors, see the <a
     *          href="../util/Formatter.html#detail">Details</a> section of the
     *          Formatter class specification.
     *
     * @throws  NullPointerException
     *          If the <tt>format</tt> is <tt>null</tt>
     *
     * @return  This writer
     *
     * @since  1.5
     */
    public PrintWriter format(String format, Object ... args) {
        try {
            synchronized (lock) {
                ensureOpen();
                if ((formatter == null)
                    || (formatter.locale() != Locale.getDefault()))
                    formatter = new Formatter(this);
                formatter.format(Locale.getDefault(), format, args);
                if (autoFlush)
                    out.flush();
            }
        } catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        } catch (IOException x) {
            trouble = true;
        }
        return this;
    }

    /**
     * Writes a formatted string to this writer using the specified format
     * string and arguments.  If automatic flushing is enabled, calls to this
     * method will flush the output buffer.
     *
     * @param  l
     *         The {@linkplain java.util.Locale locale} to apply during
     *         formatting.  If <tt>l</tt> is <tt>null</tt> then no localization
     *         is applied.
     *
     * @param  format
     *         A format string as described in <a
     *         href="../util/Formatter.html#syntax">Format string syntax</a>.
     *
     * @param  args
     *         Arguments referenced by the format specifiers in the format
     *         string.  If there are more arguments than format specifiers, the
     *         extra arguments are ignored.  The number of arguments is
     *         variable and may be zero.  The maximum number of arguments is
     *         limited by the maximum dimension of a Java array as defined by
     *         <cite>The Java&trade; Virtual Machine Specification</cite>.
     *         The behaviour on a
     *         <tt>null</tt> argument depends on the <a
     *         href="../util/Formatter.html#syntax">conversion</a>.
     *
     * @throws  java.util.IllegalFormatException
     *          If a format string contains an illegal syntax, a format
     *          specifier that is incompatible with the given arguments,
     *          insufficient arguments given the format string, or other
     *          illegal conditions.  For specification of all possible
     *          formatting errors, see the <a
     *          href="../util/Formatter.html#detail">Details</a> section of the
     *          formatter class specification.
     *
     * @throws  NullPointerException
     *          If the <tt>format</tt> is <tt>null</tt>
     *
     * @return  This writer
     *
     * @since  1.5
     */
    public PrintWriter format(Locale l, String format, Object ... args) {
        try {
            synchronized (lock) {
                ensureOpen();
                if ((formatter == null) || (formatter.locale() != l))
                    formatter = new Formatter(this, l);
                formatter.format(l, format, args);
                if (autoFlush)
                    out.flush();
            }
        } catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        } catch (IOException x) {
            trouble = true;
        }
        return this;
    }

    /**
     * Appends the specified character sequence to this writer.
     *
     * <p> An invocation of this method of the form <tt>out.append(csq)</tt>
     * behaves in exactly the same way as the invocation
     *
     * <pre>
     *     out.write(csq.toString()) </pre>
     *
     * <p> Depending on the specification of <tt>toString</tt> for the
     * character sequence <tt>csq</tt>, the entire sequence may not be
     * appended. For instance, invoking the <tt>toString</tt> method of a
     * character buffer will return a subsequence whose content depends upon
     * the buffer's position and limit.
     *
     * @param  csq
     *         The character sequence to append.  If <tt>csq</tt> is
     *         <tt>null</tt>, then the four characters <tt>"null"</tt> are
     *         appended to this writer.
     *
     * @return  This writer
     *
     * @since  1.5
     */
    public PrintWriter append(CharSequence csq) {
        if (csq == null)
            write("null");
        else
            write(csq.toString());
        return this;
    }

    /**
     * Appends a subsequence of the specified character sequence to this writer.
     *
     * <p> An invocation of this method of the form <tt>out.append(csq, start,
     * end)</tt> when <tt>csq</tt> is not <tt>null</tt>, behaves in
     * exactly the same way as the invocation
     *
     * <pre>
     *     out.write(csq.subSequence(start, end).toString()) </pre>
     *
     * @param  csq
     *         The character sequence from which a subsequence will be
     *         appended.  If <tt>csq</tt> is <tt>null</tt>, then characters
     *         will be appended as if <tt>csq</tt> contained the four
     *         characters <tt>"null"</tt>.
     *
     * @param  start
     *         The index of the first character in the subsequence
     *
     * @param  end
     *         The index of the character following the last character in the
     *         subsequence
     *
     * @return  This writer
     *
     * @throws  IndexOutOfBoundsException
     *          If <tt>start</tt> or <tt>end</tt> are negative, <tt>start</tt>
     *          is greater than <tt>end</tt>, or <tt>end</tt> is greater than
     *          <tt>csq.length()</tt>
     *
     * @since  1.5
     */
    public PrintWriter append(CharSequence csq, int start, int end) {
        CharSequence cs = (csq == null ? "null" : csq);
        write(cs.subSequence(start, end).toString());
        return this;
    }

    /**
     * Appends the specified character to this writer.
     *
     * <p> An invocation of this method of the form <tt>out.append(c)</tt>
     * behaves in exactly the same way as the invocation
     *
     * <pre>
     *     out.write(c) </pre>
     *
     * @param  c
     *         The 16-bit character to append
     *
     * @return  This writer
     *
     * @since 1.5
     */
    public PrintWriter append(char c) {
        write(c);
        return this;
    }