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Java 中方法参数的使用情况:
•一个方法不能修改一个基本数据类型的参数 (即数值型或布尔型)。
•一个方法可以改变一个对象参数的状态。
•一个方法不能让对象参数引用一个新的对象。
这三句话需要怎么理解呢?下面用具体的实例来演示这个过程:
public class PramTest {
public static void main(String[] args){
//测试一
double percent=10;
System.out.println("Before:percent="+percent);
tripleValue(percent);
System.out.println("After:percent="+percent);
System.out.println("*******************");
//测试二
Employee mike=new Employee("Mike",5000);
System.out.println("Before:salary="+mike.getSalary());
tripleSalary(mike);
System.out.println("After:salary="+mike.getSalary());
System.out.println("*******************");
//测试三
Employee a = new Employee("Alice",3000);
Employee b = new Employee("Bob",7000);
System.out.println("Before:a="+a.getName());
System.out.println("Before:b="+b.getName());
swap(a,b);
System.out.println("After:a="+a.getName());
System.out.println("After:b="+b.getName());
}
public static void tripleValue(double x){
x = 3*x;
System.out.println("End of method: x="+x);
}
public static void tripleSalary(Employee x){
x.raiseSalary(200);
System.out.println("End of method: salary="+x.getSalary());
}
public static void swap(Employee x,Employee y){
Employee temp=x;
x=y;
y=temp;
System.out.println("End of method: x="+x.getName());
System.out.println("End of method: y="+y.getName());
}
}
public class Employee {
private String name;
private double salary;
public Employee(String n,double s){
name = n;
salary = s;
}
public String getName(){
return name;
}
public double getSalary() {
return salary;
}
public void raiseSalary(double byPercent){
double raise = salary * byPercent/100;
salary +=raise;
}
}
运行结果: