eg:
class StreamTest {
public static void main(String[] args) throws Exception {
int data;
while((data=System.in.read())!=-1) {
System.out.write(data);
System.out.println(data);
}
System.out.println("Hello World!");
}
}
输入:asl
输出:
a97
s115
l108
13
10
<注意中间有空格行!!>
write()方法是字符流 println()方法是字节流
首先data=System.in.read()得到的是int型的,Sysetm.out.write(int a)是将a转换成字符,
然后输出...
Sysetm.out.println(int a)直接把a输出,不转换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。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,i
nit(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。