【作业】对于对象的课程作业

 1 class C1
 2 {
 3     private int num;
 4     public C1(int num)
 5     {
 6         this.num=num;
 7     }
 8 }
 9 public class Text_001
10 {
11     public static void main(String[] args)
12     {
13         C1 t1=new C1(100);
14         C1 t2=new C1(100);
15         System.out.println(t1==t2);
16         C1 t3=t1;
17         System.out.println(t1==t3);
18         t2=t1;
19         System.out.println(t1==t2);
20     }
21 }

结果：

false
true
true

对象在定义的时候调用了没有参数的构造函数，但是该类并不含有对应的构造函数

public class InitializeBlockDemo {

    /**
     * @param args
     */
    public static void main(String[] args) {
        
        InitializeBlockClass obj=new InitializeBlockClass();
        System.out.println(obj.field);
        
        obj=new InitializeBlockClass(300);
        System.out.println(obj.field);
    }

}

class InitializeBlockClass{
    //下面这句在初始化块之前与之后，会影响到field字段的初始值
    //public int field=100;
    
    {
        field=200;
    }
    public int field=100;
    public InitializeBlockClass(int value){
        this.field=value;
    }
    public InitializeBlockClass(){
        
    }
}

结果：

100

300

在同时有初始化块和构造方法的情况下，构造方法优先。

 1 public class Text_002
 2 {
 3 
 4     public static void main(String[] args)
 5     {
 6         int i=100;
 7         C1 t1=new C1();
 8         t1.setNum(i);//静态方法访问没有附加static的变量
 9     }
10 
11 }
12 class C1
13 {
14     private int num;
15     public void setNum(int num)
16     {
17         this.num=num;
18     }
19 }

 1 public class HowManyClassYouHaveCreated
 2 {
 3 
 4     public static void main(String[] args)
 5     {
 6         int f=1;
 7         Hello h1=new Hello();
 8         Hello h2=new Hello();
 9         Hello h3=new Hello();
10         Hello h4=new Hello();
11         Hello h5=new Hello();
12         Hello h6=new Hello();
13         Hello h7=new Hello();
14         System.out.println("HowManyClassYouHaveCreated?");
15         System.out.println(h7.getNum());
16         
17     }
18 
19 }
20 class Hello
21 {
22     static private int num=0;
23     public Hello()
24     {
25         System.out.println("Hello");
26         num++;
27     }
28     public int getNum()
29     {
30         return num;
31     }
32 }