java虚拟机类的加载顺序

浅浅的花香味﹌ 2022-09-19 10:56 116阅读 0赞

Parent.java

![None.gif][] package  book.oo.initorder;  
![None.gif][]  
![None.gif][] public   class  Parent  
![ExpandedBlockStart.gif][]![ContractedBlock.gif][] ... \{  
![InBlock.gif][]    private int ix = 50;  
![InBlock.gif][]  
![InBlock.gif][]    private static int iz = getNext(30);  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Parent的初始化块");  
![InBlock.gif][]        int x = 100;  
![InBlock.gif][]        int y = 100; // getNext(100);  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]    static  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Parent的静态初始化块");  
![InBlock.gif][]        int sx = 100;  
![InBlock.gif][]        int sy = getNext(100);  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]  
![InBlock.gif][]    private int endall = 1;  
![InBlock.gif][]  
![InBlock.gif][]    public Parent()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Parent的构造方法被调用");  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]  
![InBlock.gif][]    public void display()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Parent的display方法被调用");  
![InBlock.gif][]        System.out.print("ix=" \+ this.ix);  
![InBlock.gif][]        System.out.println("; iz=" \+ iz);  
![InBlock.gif][]        dispA();  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]  
![InBlock.gif][]    public static void dispA()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Parent的dispA()被调用");  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]  
![InBlock.gif][]    public static int getNext(int base)  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Parent的getNext(int base)被调用");  
![InBlock.gif][]        return \++base;  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    /\*\* \*//\*\*  
![InBlock.gif][]     \* 当Java在进行垃圾回收时，会调用对象的finalize方法  
![ExpandedSubBlockEnd.gif][]     \*/  
![InBlock.gif][]    protected void finalize()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Parent的销毁方法被调用");  
![ExpandedSubBlockEnd.gif][]    \}  
![ExpandedBlockEnd.gif][]\}

Child.java

![None.gif][] package  book.oo.initorder;  
![None.gif][]  
![None.gif][] public   class  Child  extends  Parent  
![ExpandedBlockStart.gif][]![ContractedBlock.gif][] ... \{  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Child的初始化块");  
![InBlock.gif][]        int bx = 100;  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]    static  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Child的静态初始化块");  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]  
![InBlock.gif][]    public Child()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        super();  
![InBlock.gif][]        System.out.println("Child的构造方法被调用");  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]  
![InBlock.gif][]    public static void dispB()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Child的dispB()被调用");  
![ExpandedSubBlockEnd.gif][]    \}  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    /\*\* \*//\*\*  
![InBlock.gif][]     \* 当Java在进行垃圾回收时，会调用对象的finalize方法  
![ExpandedSubBlockEnd.gif][]     \*/  
![InBlock.gif][]    protected void finalize()  
![ExpandedSubBlockStart.gif][]![ContractedSubBlock.gif][]    ...\{  
![InBlock.gif][]        System.out.println("Child的销毁方法被调用");  
![InBlock.gif][]        super.finalize();  
![ExpandedSubBlockEnd.gif][]    \}  
![ExpandedBlockEnd.gif][]\}

ClassInitOrderTest.java

![None.gif][] package  book.oo.initorder;  
![None.gif][]  
![None.gif][] public   static   void  main(String\[\] args)  
![ExpandedBlockStart.gif][]![ContractedBlock.gif][] ... \{  
![InBlock.gif][]    System.out.println("不new对象，访问静态方法时的输出：");  
![InBlock.gif][]    Child.dispB();  
![InBlock.gif][]  
![InBlock.gif][]    System.out.println();  
![InBlock.gif][]    System.out.println("new对象，访问非静态方法时的输出：");  
![InBlock.gif][]    new Child().display(); //通知虚拟机进行垃圾回收 System.gc();  
![InBlock.gif][]  
![ExpandedBlockEnd.gif][]\}   
![None.gif][]

以上代码摘抄自 JAVA JDK实例宝典,但书中关于JAVA类的加载部分有误,但代码可用来作测试,了解类的加载顺序

当一个类或它的子类调用它的静态方法时,如上面的Child.dispB(),虚拟机会先初始化类的静态变量,静态初始化块,其初始化顺序按照变量和初始化块在程序中的位置来决定,依次按排在前面到后面的顺序初始化,初始化静态变量和静态初始化块的顺序没有先后之分,但不会初始化烊的静态方法.如Child.dispB()这样访问类的静态方法的时候,不会初始化类的初始化块,构造函数,普通变量等.

当一个类new一个对象时,会按先父类后子类的顺序初始化类的,静态变量,静态初始化块,普通变量,普通初始化块,构造函数等.

[None.gif]: /images/20220828/712c8993881d4022962b129417b8bd39.png
[ExpandedBlockStart.gif]: http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedBlockStart.gif
[ContractedBlock.gif]: /images/20220828/1c3bd543e653427a90ca6cd580bba545.png
[InBlock.gif]: /images/20220828/d0877c3629704ab4a42e99c3b3134e15.png
[ExpandedSubBlockStart.gif]: http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubBlockStart.gif
[ContractedSubBlock.gif]: /images/20220828/00fa9a84c6a54aacbe3d47bfd328b463.png
[ExpandedSubBlockEnd.gif]: /images/20220828/6f40d82f3c3d4db19522f5f95219ca5f.png
[ExpandedBlockEnd.gif]: /images/20220828/5fc96ce4414444f2ba8e642c1a2ec4bc.png