介绍

• System是一个final类，使用频率非常高的工具类
• JDK之java.lang.System
• Java中native关键字的作用

源码

构造函数

/** Don't let anyone instantiate this class */
private System() {
}

静态代码块

private static native void registerNatives();

static {
    registerNatives();
}

成员变量

public final static InputStream in = null;
public final static PrintStream out = null;
public final static PrintStream err = null;
private static volatile SecurityManager security = null;
private static volatile Console cons = null;

成员方法

// 返回毫秒数
public static native long currentTimeMillis();
//返回纳秒，但是该函数只能用于计算时间差
public static native long nanoTime();
//Runs the garbage collector.
public static void gc() {
    Runtime.getRuntime().gc();
}
public static native void arraycopy(Object src,  int  srcPos,
                                    Object dest, int destPos,
                                    int length);
@CallerSensitive
public static void load(String filename) {
    Runtime.getRuntime().load0(Reflection.getCallerClass(), filename);
}

public static void exit(int status) {
    Runtime.getRuntime().exit(status);
}