Java笔记——finalize、static、abstract、final、this关键字

淡淡的烟草味﹌ 2022-05-29 10:07 195阅读 0赞

1、对象的生命周期
    
    （1）finalize
    
    package cn.sdut;
    
    public class AA {
    
     int x=100;
     int y=100;
     
     public AA() {
      x=10;
      y=20;
     }
     
     public AA(int x, int y) {
      super();
      this.x = x;
      this.y = y;
     }
     
    
     
     
     @Override
     protected void finalize() throws Throwable {
      System.out.println("AA finalize......");  
      super.finalize();
     }
    
     public void mm()
     {
      System.out.println(x+"=="+y);
     }
     
     public static void main(String[] args) {
      AA aa=new AA();
      aa.mm();
      //................
      
      aa=null;
      
      System.gc();
     }
    }
    
    //（2）static
    
    package cn.sdut;
    
    public class AA {
    
     static{  //静态代码块   一个程序中，静态代码块会最先执行
      System.out.println("static block ......");
     }
     
     
     static  int x=100;  //类变量，静态变量
      int y=100;
     
     public AA() {
      
      y=20;
     }
     
     public AA(int x, int y) {
      super();
      this.x = x;
      this.y = y;
     }
     
     @Override
     protected void finalize() throws Throwable {
      System.out.println("AA finalize......");  
      super.finalize();
     }
    
     public static void mm()    //类方法，静态方法
     {
         System.out.println(x+"==");
     }
     
     public static void main(String[] args) {
      AA aa=new AA();
         System.out.println(AA.x);
         x+=20;
         AA bb=new AA();
         System.out.println(AA.x);
         System.out.println(AA.x);
         AA.mm();
     }
    }
    
    //2、abstract
    
    //（1）抽象类不能实例化；（2）抽象类里面可以定义抽象方法，也可以定义非抽象方法；（3）含有抽象方法的类一定是抽象类。
    
    package cn.sdut;
    
    public abstract class AA {
    
     static{
      System.out.println("static block ......");
     }
     
     
     static  int x=100;
      int y=100;
     
     public AA() {
      
      y=20;
     }
     
     public AA(int x, int y) {
      super();
      this.x = x;
      this.y = y;
     }
     
     @Override
     protected void finalize() throws Throwable {
      System.out.println("AA finalize......");  
      super.finalize();
     }
    
     public abstract void mm();
     public void mm2(){};
     
     public static void main(String[] args) {
      
     }
    }
    
    3、final
    
    修饰变量，赋值次数只有1次；
    
    修饰方法，子类不能重写（覆盖）方法。
    
    package cn.sdut;
    
    public  class AA {
     
        final int x;
     int y=100;
     
     public AA() {
      x=20;
      y=20;
     }
     
     public AA(int x, int y) {
      super();
      this.x = x;
      this.y = y;
     }
    
    
     public final void mm2(){};
     
     public static void main(String[] args) {
      final int a=10;
      
     }
    }
    
    4、this
    
    package cn.sdut;
    
    public  class AA {
     
        final int x;
     int y=100;
     int z;
     
     public AA() {
      this(20,20); 
      z=10;  
     }
     
     public AA(int x, int y) {
      this.x = x;
      this.y = y;
     }
    
    
     public  void mm2(){
      System.out.println(this.x+"=="+this.y);
     };
     
     public  void mm3(){
      this.mm2();
     };
     
     public static void main(String[] args) {
     }
    }