Java 方法 对象参数

/**
   @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;
      System.out.println("swap method: Employee temp.name=" + temp.getName() + " temp.salary=" + temp.getSalary() );
      x = y;
      y = temp;
      System.out.println("End of method: x=" + x.getName());
      System.out.println("End of method: y=" + y.getName());
      System.out.println("swap method: Employee temp.name=" + temp.getName() + " temp.salary=" + temp.getSalary() );
      
   }
}

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;
}

 

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

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

Testing swap:
Before: a=Alice
Before: b=Bob
swap method: Employee temp.name=Alice temp.salary=70000.0
End of method: x=Bob
End of method: y=Alice
swap method: Employee temp.name=Alice temp.salary=70000.0
After: a=Alice
After: b=Bob