同情心123
幼苗
共回答了15个问题采纳率:93.3% 举报
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(char c) {
write(String.valueOf(c));
}
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.
System.out.write(a); 调用的是PrintStream.write(int b)方法
write(int b) 的源代码如下:
public void write(int b) {
try {
synchronized (this) {
ensureOpen();
out.write(b);
if ((b == 'n') && autoFlush)
out.flush();
}
}
catch (InterruptedIOException x) {
Thread.currentThread().interrupt();
}
catch (IOException x) {
trouble = true;
}
}
看过源代码后应该明白两者之间的差异了,println(String s)不但会刷新out,而且还会同时刷新textOut和charOut,而write(int b)只有当b == 'n'时才刷新out.这也是为什么加了System.out.write('n'); 后就能显示出来了,问题就在于out没有刷新.
楼主的第二个问题很好解释,因为在print(String s)中,会刷新textOut和charOut.
textOut和charOut是什么?看一下PrintStream中的定义:
private BufferedWriter textOut;
private OutputStreamWriter charOut;
textOut和charOut在init(OutputStreamWriter osw)方法中初始化,init(OutputStreamWriter osw)的代码如下:
private void init(OutputStreamWriter osw) {
this.charOut = osw;
this.textOut = new BufferedWriter(osw);
}
init()函数在构造函数中被调用
public PrintStream(OutputStream out, boolean autoFlush) {
this(autoFlush, out);
init(new OutputStreamWriter(this));
}
可见,textOut和charOut操作的输出流和out是一样的,因此对textOut和charOut刷新同时刷新了out,因此print(String s)即便没有'n',也同样会直接输出出来.
1年前
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