System是System類
1 package java.lang;
2 public final class System {
3 public final static PrintStream out = null;
4 }
println()是PrintStream 類中的方法。
package java.io;
public class PrintStream extends FilterOutputStream
implements Appendable, Closeable
{
protected OutputStream out;
private BufferedWriter textOut;
private void ensureOpen() throws IOException {
if (out == null)
throw new IOException("Stream closed");
}
public void println() {
newLine();//換行
}
public void println(boolean x) {
synchronized (this) {
print(x);
newLine();
}
}
public void println(String x) {
synchronized (this) {
print(x);
newLine();
}
}
public void print(boolean b) {
write(b ? "true" : "false");
}
public void print(Object obj) {
write(String.valueOf(obj));
}
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;
}
}
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;
}
}
}
轉載于:https://www.cnblogs.com/stujike/p/9688054.html