javz笔记之：有趣的静态方法的使用

import java.util.*;

public class welcome {

    public static void main(string[] args)
       {
          /*
           * test 1: methods can't modify numeric parameters
           */
          system.out.println("testing triplevalue:");
          double percent = 10;
          system.out.println("before: percent =" + percent);
          percent = triplevalue(percent);
          system.out.println("after: percent =" + percent);  //这里输出为30了！正常的结果

          /*
           * test 2: methods can change the state of object parameters
           */
          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
           */
          system.out.println("\ntesting swap:");
          employee a = new employee("alice", 70000);
          employee b = new employee("bob", 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 double triplevalue(double x) // doesn't work
       {
          return x = 3 * x;
          //system.out.println("end of method: x=" + x);
       }

       public static void triplesalary(employee x) // works
       {
          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());
       }
    }

    class employee // simplified employee class
    {
       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;
       }

       private string name;
       private double salary;
    }

如果是以下代码：system.out.println("after: percent =" + percent);  //这里输出为10了！因为静态方法达不成你要的效果

这是因为静态方法不能对对象产生效果，和静态域一样，它属于类，不属于任何对象。

/**
 * this program demonstrates parameter passing in java.
 * @version 1.00 2000-01-27
 * @author cay horstmann
 */
public class paramtest
{
   public static void main(string[] args)
   {
      /*
       * test 1: methods can't modify numeric parameters
       */
      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
       */
      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
       */
      system.out.println("\ntesting swap:");
      employee a = new employee("alice", 70000);
      employee b = new employee("bob", 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) // works
   {
      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());
   }
}

class employee // simplified employee class
{
   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;
   }

   private string name;
   private double salary;
}