java===java基础学习（9）---方法参数

 方法参数注意三要点：

一个方法不能修改一个基本数据类型的参数（数值型或者布尔型）。

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。

 

package testbotoo;

public class ParamTest{
    

    public static void main(String[] args)
    {
        /*
         * Test 1 :Methods cant't modify numeric parameers
         */
        System.out.println("Testing tripleValue");
        double percent = 10;
        System.out.println("before:percent="+percent);
        tripleValue(percent);
        System.out.println("after:perent="+percent);
        
        /*
         *  Test2 ：Methods can change the state of object parameters
         */
        System.out.println("
Testing tripleSalary:");
        Empl harry = new Empl("harry", 5000);
        System.out.println("
 before salary = "+ harry.getSalary());
        tripleSalary(harry);
        System.out.println("after salary = "+ harry.getSalary());
        
        
        /*
         * Test 3 : nethods can't attach new objects to objects parameters
         */
        
        System.out.println("
testing swap:");
        Empl a = new Empl("sss",500);
        Empl b = new Empl("bob", 600);
        System.out.println("befoer: a = "+ a.getName());
        System.out.println("befoer: 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)//dosen't work
    {
        x = 3*x;
        System.out.println("x="+x);
    }
    
    public static void tripleSalary(Empl x) //works
    {
        x.raiseSalary(200);
        System.out.println("end of method : salary = "+ x.getSalary());
        
    }
    
    public static void swap(Empl x ,Empl y)
    {
        Empl temp = x;
        x = y ;
        y = temp;
        System.out.println("x = "+ x.getName());
        System.out.println("y = "+ y.getName());
    }
    
}    
    
class Empl
{
    
    private String name;
    private double salary;
    
    public Empl(String n, double s)
    {
        name = n;
        salary = s;
    }
    
    public String getName()
    {

        return name;
    }
    
    public double getSalary()
    {
        return salary;
    }
    
    public void raiseSalary(double byPrecent)
    {
        double raise = salary * byPrecent /100;
        salary += raise;
    }
}