Java 值传递与引用传递

值传递：就是方法调用时，实际参数把它的值传递给对应的形式参数，方法中执行形式参数值的改变不影响实际参数的值。
引用传递(传地址)：就是方法调用时，实际参数的引用(即地址，而不是参数的值)被传递给方法中相对应的形式参数，在方法执行时对形式参数的操作实际上就是对实际参数的操作（地址操作），这样方法执行中形式参数值的改变将会影响实际参数的值。

值传递——基本数据类型作为参数（如：int , String）

public class Test{

public static void change(int a,int b){

int temp = a;

a = b;

b = temp;

}

public static void main(String[] args){

int a = 12;

int b = 23;

System.out.println(a+","+b);

change(a,b);

System.out.println(a+","+b);

}

}

执行结果：
12,23

12,23

由此可见，在方法执行之前和之后a,b的值并没有改变。

引用传递——对象（引用地址）作为参数（如：Person）

public class Test1{

public static void main(String[] args){

Person person = new Person("刘备",100);

System.out.println("name = " + person.name + "; age = " + person.age);

person.changePerson(person,"关羽",88);

System.out.println("name = " + person.name + "; age = " + person.age);

}

}

class Person{

String name;

int age;

public Person(String name, int age){

this.name = name;

this.age = age;

}

public void changePerson(Person person, String name, int age){

person.name = name;

person.age = age;

}

}

执行结果：

name = 刘备; age = 100

name = 关羽; age = 88

由此可见：形式参数的值的改变影响了实际参数的值

综合示例：

package homework;

public class Test1 {

public static void main(String []args){

// 对象，引用传递

Person person = new Person("刘备", 100);

System.out.println("name = " + person.name + "; age = " + person.age);

person.changePerson(person, "张飞", 78);

System.out.println("name = " + person.name + "; age = " + person.age);

// String类型，值传递

String name1 = "曹操";

String name2 = "项羽";

System.out.println("name1 = " + name1 + "; name2 = " + name2);

changeString(name1, name2);

System.out.println("name1 = " + name1 + "; name2 = " + name2);

// int类型，值传递

int a = 34;

int b = 45;

System.out.println("a = " + a + "; b = " + b);

change(a, b);

System.out.println("a = " + a + "; b = " + b);

}

// String类型

public static void changeString(String name1, String name2){

String temp;

temp = name1;

name1 = name2;

name2 = temp;

}

// int类型

public static void change(int a, int b){

int temp;

temp = a;

a = b;

b = temp;

}

}

class Person{

String name;

int age;

public Person(String name, int age){

this.name = name;

this.age = age;

}

public void changePerson(Person person, String name, int age){

person.name = name;

person.age = age;

}

}

运行结果：

name = 刘备; age = 100

name = 张飞; age = 78

name1 = 曹操; name2 = 项羽

name1 = 曹操; name2 = 项羽

a = 34; b = 45

a = 34; b = 45