该类用于验证类的初始化时机

output.txt

调用非自己声明的方法，不会执行类初始化
Class TechnequeGuy initialized
Person says, 'I'm a techneque guy'
---------------
给非自己声明的静态域赋值，不会执行类初始化
---------------
访问自己声明的常量，不会执行类初始化
Programmer is really cute? Yes
---------------
以反射方式调用自己声明的静态方法，会执行类初始化
Class Programmer initialized
Programmer says 'bla bla bla...'
---------------
以反射方式调用非自己声明的静态方法，不会执行类初始化
Person says, 'I'm a techneque guy'
---------------

TestClassInitialization.java

package problem.java.lang.klass;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

/**
 * 该类用于验证类的初始化时机
 * 
 * 具体时机参见JLS  http://docs.oracle.com/javase/specs/jls/se7/html/jls-12.html#jls-12.4.1
 *
 */
public class TestClassInitialization {

    public static void main(String[] args) throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        //调用非自己声明的方法，不会执行类初始化
        System.out.println("调用非自己声明的方法，不会执行类初始化");
        Programmer.print();
        System.out.println("---------------");
        
        //给非自己声明的静态域赋值，不会执行类初始化
        System.out.println("给非自己声明的静态域赋值，不会执行类初始化");
        Programmer.isSmart = true;
        System.out.println("---------------");
        
        //访问自己声明的常量，不会执行类初始化
        System.out.println("访问自己声明的常量，不会执行类初始化");
        System.out.println("Programmer is really cute? " + (Programmer.isCute?"Yes":"Noe"));
        System.out.println("---------------");
        
        //以反射方式调用自己声明的静态方法，会执行类初始化
        System.out.println("以反射方式调用自己声明的静态方法，会执行类初始化");
        Class<?> programmerClass = Programmer.class;
        Method talkMethod = programmerClass.getMethod("talk", ( Class<?>[])null);
        talkMethod.invoke(programmerClass, (Object[])null);
        System.out.println("---------------");
        
        //以反射方式调用非自己声明的静态方法，不会执行类初始化
        System.out.println("以反射方式调用非自己声明的静态方法，不会执行类初始化");
        Class<?> programmerAmateurClass = Programmer.class;
        Method printMethod = programmerAmateurClass.getMethod("print", ( Class<?>[])null);
        printMethod.invoke(programmerAmateurClass, (Object[])null);
        System.out.println("---------------");
        
        //暂时还没想到单纯靠断言启动类初始化的方法
    }

}

interface Person {
}

class TechnequeGuy implements Person {
    public static boolean isSmart = false;
    
    static {
        System.out.println("Class TechnequeGuy initialized");
    }
    
    public static void print() {
        System.out.println("Person says, 'I'm a techneque guy'");
    }
}

class Programmer extends TechnequeGuy implements Person {
    public static final boolean isCute = true;
    
    public static void talk() {
        System.out.println("Programmer says 'bla bla bla...'");
    }
    
    static {
        System.out.println("Class Programmer initialized");
    }
}

class ProgrammingAmateur extends Programmer implements Person {
    public static boolean isRealyRealyCute = true;
    
    static {
        boolean isRealyCute = true;
        assert isRealyCute != false;
        if (isRealyCute) {
            System.out.println("Class ProgrammingAmateur initialized, and he's really cute");
        }
    }
}