Java, swap FAQ

 

  

directly on the code ......

  

   

public class Swap { 
 
    public static void main(String[] args) { 
        int a[] = new int[]{1,2}; 
        System.out.println(a[0] + " "+a[1]); 
        swap(a,0,1); 
        System.out.println(a[0] + " "+a[1]); 
 
    } 
private static void swap(int[] a, int i, int j) { 
         
        int temp = a[i]; 
        a[i] = a[j]; 
        a[j] = temp; 
    } 
}

  

 

 

  

method call (call by) is a standard computer scientific terms , the method call according to the parameters passed value of the case is divided into call (call by reference) , and reference calls ( call by value ). There are many rivers and lakes on the definition of these two calls , the most common argument is passed value is a value call delivery address is referenced calls. This is actually very appropriate , that these claims are easy to make we associate a Java object parameter passing is call by reference in fact , Java's object parameter passing value is still called. In the main output or the original 2,3 years , regardless of reference type is passed also is the object instance.

  

   

public class Swap1 
{ 
    public static void main(String[] args) 
    { 
        Integer a=new Integer(2); 
        Integer b=new Integer(3); 
        TestSwap ts=new TestSwap(a,b); 
        System.out.println("before swap:"); 
        ts.outPut(); 
        ts.dataSwap1(a,b); 
        System.out.println("after swap:"); 
        ts.outPut(); 
    } 
} 
 
class TestSwap 
{ 
    Integer a=null; 
    Integer b=null; 
     
    public TestSwap(Integer a,Integer b) 
    { 
        this.a=a; 
        this.b=b; 
    } 
    /*这样不可交换,交换的只是拷贝过来的引用，而 
     * 输出还是成员变量(输出用的是类内的方法) 
     * 重要的是，形参和实参所占的内存地址并不一样， 
     * 形参中的内容只是实参中存储的对象引用的一份拷贝。 
     * */ 
    protected void dataSwap0(Integer a,Integer b) 
    { 
        Integer temp=a; 
        a=b; 
        b=temp; 
    } 
    protected void dataSwap(Integer a,Integer b) 
    { 
        this.a = b; 
        this.b = a; 
    } 
    //这样也可以，不过需要类内的输出，就是说输出TestSwap的成员变量 
    protected void dataSwap1(Integer a,Integer b) 
    { 
        Integer temp=this.a; 
        this.a=this.b; 
        this.b=temp; 
    } 
    protected void outPut() 
    { 
        System.out.println("a="+a+" b="+b); 
    }  
}