main.java

java的经典例子

public class Main {
    public static void main(String[] args) {
        MySecurityManager sm = new MySecurityManager();

        System.setSecurityManager(sm);
        sm.printClassDepth("C");                      // -1
        sm.printClassDepth("MySecurityManager");      // 0
        sm.printClassDepth("Main");                   // 1

        C.printClassDepth("C");                       // 1
        C.printClassDepth("MySecurityManager");       // 0
        C.printClassDepth("Main");                    // 2
    }
}

class MySecurityManager extends SecurityManager {
    public void printClassDepth(String name) {
        System.out.println(classDepth(name));
    }
}

class C {
    static void printClassDepth(String name) {
        ((MySecurityManager) 
         System.getSecurityManager()).printClassDepth(name);
    }
}