Java中方法参数使用

关于Java中方法参数的使用情况：

• 1一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)。 –> 见ParamTest之Test 1
• 2一个方法可以改变一个对象参数的状态。–> 见ParamTest之Test 2
• 3一个方法不能让对象参数引用一个新的对象。–>见ParamTest之Test 3

ParamTest.java：

/**
 *This program demonstrates parameter passing in Java.
 *@version 1.01 2016-12-28
 *@author NPJ
*/

public class ParamTest {
    public static void main(String[] args) {

        /*
              *Test 1: Methods can't modify numeric parameters 
              *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)
              */    

         System.out.println("Testing tripleValue:");
         double percent = 10;
         System.out.println("Before:percent=" + percent);
         tripleValue(percent);
         System.out.println("After:percent=" + percent);

         /*
               *Test 2: Methods can change the state of object parameters
               *一个方法可以改变一个对象参数的状态
               */

         System.out.println("\nTesting tripleSalary:");
         Employee harry = new Employee("Harry",50000);
         System.out.println("Before:salary=" + harry.getSalary());
         tripleSalary(harry);
         System.out.println("After:salary=" + harry.getSalary());

         /*
               *Test 3:Methods can't attach new objects to object parameters
               *一个方法不能让对象参数引用一个新的对象
               */

          System.out.println("\nTesting swap:");
          Employee a = new Employee("Alice",70000);
          Employee b = new Employee("Bod",60000);
          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) { //doesn't work
            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 mehod:salary=" +     x.getSalary()); 
    } 

    public static void swap(Employee x,Employee y) {
            Employee temp;
            temp = x;
            x = y;
            y = temp;
            System.out.println("End of method:x=" + x.getName());
            System.out.println("End of method:y=" + y.getName());   
   }
}

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;    
    }
}


/*      
    Testing tripleValue:
    Before:percent=10.0
    End of method:x=30.0
    After:percent=10.0

    Testing tripleSalary:
    Before:salary=50000.0
    End of mehod:salary=150000.0
    After:salary=150000.0

    Testing swap:
    Before:a=Alice
    Before:b=Bod
    End of method:x=Bod
    End of method:y=Alice
    After:a=Alice
    After:b=Bod
*/