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());
   }
 
   private 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());
   }
 
   private static void tripleSalary(Employee x) {
     x.raiseSalary(200);
     System.out.println("End of method: salary=" + x.getSalary());
   }
 
   private static void tripleValue(double x) {
     x=3*x;
     System.out.println("End of Method X= "+x);
   }
 }

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
End of method: x=Bob //可见引用的副本进行了交换
End of method: y=Alice
After: a=Alice //引用本身没有交换
After: b=Bob