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("\nTesting tripleSalary:");
Empl harry = new Empl("harry", 5000);
System.out.println("\n 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("\ntesting 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;
}
}