类加载顺序

package com.ai.common;

public class StaticInit {
    
    
    private static class StaticPa{
        static final int high2 =13;
        final int high3 = print("Init StaticPa variable high3");
        static {
            System.out.println("StaticPa static block: "+high2);
        }
        private StaticPa(int a){
            System.out.println("StaticPa constructor: "+a);
        }
        
        public static int print(String str){
            System.out.println(str);
            return 0;
        }
    }
    
    private static class StaticTest extends StaticPa{
        static final int final1 = 123;
        static final double final2 =  234d;
        static final String final3 = "222";
        static final String final4 = new String("final4");
        final int high4 = print("Init StaticTest variable high4");
        static {
            System.out.println("StaticTest static block: "+final4);
        }

        public static void test(){
            System.out.println("static method");
        }
        private StaticTest(int a){
            super(a);
            System.out.println("StaticTest constructor: "+a);
        }
    }
    
    
    public static void main(String[] args) {
        System.out.println("Before StaticTest.final1");
        Object temp = StaticTest.final1;
        System.out.println("After StaticTest.final1");

        System.out.println();
        System.out.println("Before StaticTest.final2");
        temp = StaticTest.final2;
        System.out.println("After StaticTest.final2");

        System.out.println();
        System.out.println("Before StaticTest.final3");
        temp = StaticTest.final3;
        System.out.println("After StaticTest.final3");
        
        System.out.println();
        System.out.println("Before StaticTest.final4");
        temp = StaticTest.final4;
        System.out.println("After StaticTest.final4");
        
        System.out.println();
        System.out.println("Before StaticTest.test()");
        StaticTest.test();
        System.out.println("After StaticTest.test()");
        
        System.out.println();
        System.out.println("Before StaticTest.test()");
        StaticTest.test();
        System.out.println("After StaticTest.test()");
        
        System.out.println();
        System.out.println("Before new StaticTest()");
        StaticTest st = new StaticTest(111);
        System.out.println("After new StaticTest()");
    }

}

执行后

对于Static final的基本数据类型常量 以及 Static final的String常量调用 不会导致类初始化;

对于其它任何static Field/Method/调用都会初始化类静态Field与静态代码块, 顺序为 父类Static Field/Block(自上而下顺序加载) --> 子类Static Field/Block(自上而下顺序加载)

        System.out.println("Before StaticTest.final1");
        Object temp = StaticTest.final1;
        System.out.println("After StaticTest.final1");

        System.out.println();
        System.out.println("Before StaticTest.final2");
        temp = StaticTest.final2;
        System.out.println("After StaticTest.final2");

        System.out.println();
        System.out.println("Before StaticTest.final3");
        temp = StaticTest.final3;
        System.out.println("After StaticTest.final3");
        
        System.out.println();
        System.out.println("Before StaticTest.final4");
        temp = StaticTest.final4;
        System.out.println("After StaticTest.final4");

Print:
Before StaticTest.final1
After StaticTest.final1

Before StaticTest.final2
After StaticTest.final2

Before StaticTest.final3
After StaticTest.final3

Before StaticTest.final4
StaticPa static block: 13
StaticTest static block: final4
After StaticTest.final4

　　　　　//调用静态method
        System.out.println();
        System.out.println("Before StaticTest.test()");
        StaticTest.test();
        System.out.println("After StaticTest.test()");

Print:
Before StaticTest.test()
StaticPa static block: 13
Init StaticTest variable high4
StaticTest static block: final4
static method
After StaticTest.test()

调用Constructor初始化顺序为:　父类Static Field/Block --> 子类Static Field/Block --> 父类non-static Field/Block -->父类Constructor --> 子类non-static Field/Block --> 子类Constructor

        //调用Constructor
        System.out.println();
        System.out.println("Before new StaticTest()");
        StaticTest st = new StaticTest(111);
        System.out.println("After new StaticTest()");

Print:
Before new StaticTest()
Init StaticPa variable high3
StaticPa constructor: 111
StaticTest constructor: 111
After new StaticTest()