System.out的初始值为null，为啥使用System.out.println()时系统不报空指针异常呢？

Question

不理解啊。。。以下是API中PrintStream中的成员变量out

    public final static PrintStream out = null;

Answer 1

public final class System {

    /* register the natives via the static initializer.
     *
     * VM will invoke the initializeSystemClass method to complete
     * the initialization for this class separated from clinit.
     * Note that to use properties set by the VM, see the constraints
     * described in the initializeSystemClass method.
     */
    private static native void registerNatives();
    static {
        registerNatives();
    }

看下System的源码，有初始化方法啊...

Answer 2

System.out这个值其实可以由System.setOut()这个方法来设定的，它其实是个native的方法。
Java代码前面加了final只是让用户无法赋值而已。