Java 按值传递理解(一看就懂 含具体代码说明)

1.Java总是按值调用( 即方法得到的总是参数值的拷贝（副本） )

2.Java数据类型

3.说明：

(1)基本数据类型的副本更改不影响原值

public static void main(String []args)
	{
    
    
		int value1=10;
		int value2=20;
		System.out.println("Before swap   value1: "+value1+"  value2: "+value2);//
		swap(value1, value2);
		System.out.println("After  swap   value1: "+value1+"  value2: "+value2);
	}
	public static void swap(int value1,int value2)
	{
    
    
		int temp=value1;
		value1=value2;
		value2=temp;
	}

//输出
//Before swap   value1: 10  value2: 20
//After  swap   value1: 10  value2: 20

(2)引用数据类型的副本更改不影响原引用

class Student
{
    
    
	int No;
	String name;
	public Student(int No,String name)
	{
    
    
		this.No=No;
		this.name=name;
	}
	public String toString()
	{
    
    
		return "Student [No=" + No + ", name=" + name + "]";
	}	
}
public static void main(String []args)
	{
    
    
		Student s1=new Student(10,"Alice");
		Student s2=new Student(20,"Tom");

		System.out.println("Before swap   s1: "+s1+"  s2: "+s2);
		swap(s1, s2);
		System.out.println("After  swap   s1: "+s1+"  s2: "+s2);
	}
	public static void swap(Student s1,Student s2)
	{
    
    
		Student temp=s1;
		s1=s2;
		s2=temp;
	}
//输出
//Before swap   s1: Student [No=10, name=Alice]  s2: Student [No=20, name=Tom]
//After  swap   s1: Student [No=10, name=Alice]  s2: Student [No=20, name=Tom]

(3)通过副本引用对该对象进行了更改，那么会影响到原引用。(因为副本引用和原引用指向同一对象)

public static void main(String []args)
	{
    
    
		Student s1=new Student(10,"Alice");
		Student s2=new Student(20,"Tom");

		System.out.println("Before ChangeNo   s1: "+s1);
		ChangeNo(s1);
		System.out.println("After  ChangeNo   s1: "+s1);
		System.out.println("Before ChangeNo   s2: "+s2);
		ChangeNo(s2);
		System.out.println("After  ChangeNo   s2: "+s2);
	}
	public static void ChangeNo(Student s)
	{
    
    
		 s.No=s.No+1;
	}
//输出
// Before ChangeNo   s1: Student [No=10, name=Alice]
// After  ChangeNo   s1: Student [No=11, name=Alice]
// Before ChangeNo   s2: Student [No=20, name=Tom]
// After  ChangeNo   s2: Student [No=21, name=Tom]