Java System

System.out

System.out的类型为PrintStream；
System.out.println(‘a’);
实际上调用是PrintStream的println(char c)方法；
而println(char c)方法的源代码为：

public void println(String x) {    synchronized (this) {        print(x);        newLine();    }}

可见Println调用了print(char c)方法，print(char c)方法的源代码如下：

public void print(String s) {    if (s == null) {        s = "null";    }    write(s);}

可见调用的是write(String s)方法，write(String s)的代码为：

private void write(String s) {    try {        synchronized (this) {            ensureOpen();            textOut.write(s);            textOut.flushBuffer();            charOut.flushBuffer();            if (autoFlush && (s.indexOf('\n') >= 0))                out.flush();        }    }    catch (InterruptedIOException x) {        Thread.currentThread().interrupt();    }    catch (IOException x) {        trouble = true;    }}

当字符串中含有’\n’时会刷新out，此处的out是OutStream对象的实例。println(String s)最后调用newLine() 方法，newLine()的代码如下:

private void newLine() {    try {        synchronized (this) {            ensureOpen();            textOut.newLine();            textOut.flushBuffer();            charOut.flushBuffer();            if (autoFlush)                out.flush();        }    }    catch (InterruptedIOException x) {        Thread.currentThread().interrupt();    }    catch (IOException x) {        trouble = true;    }}

newLine()会刷新out。