How to swap object s1 and s3 in attched StudentTest.java file

Below is a StudentTest class which uses Student.java to create student

Student class

class Student
 {
    int id;
    static int computeCount;

    int age;
    String name;
    String gender;
    short rank;
    double gpa;
    long phone;
    char degree;

    boolean international;
    double tutionfees=12000;
    double internationalFees=5000;

    Student(int id,String name,String gender,int age,long phone,double gpa, char degree){
      // id=newId;
      // name=newName;
      // gender=newGender;
      // age=newAge;
      // phone=newPhone;
      // gpa=newGpa;
      // degree=newDegree;
      this(id,name,gender, age, phone,gpa,degree,false);    // delegate to second parameterized constructor 
      //international=isInternational;
    }


    // Second parameterized constructor
    Student(int id,String name,String gender,int age,long phone,double gpa, char degree,boolean international){
      this.id=id;
      this.name=name;
      this.gender=gender;
      this.age=age;
      this.phone=phone;
      this.gpa=gpa;
      this.degree=degree;
      this.international=international;
}

StudentTest class

class StudentTest {
	 public static void main(String args[])
     {
        Student s1=new Student(1000,"John","Male",18,2234567890L,3.8,'B');
        Student s2=new Student(1001,"Indresh","Male",20,2234567893L,4.0,'C',true);
        Student s3 = new Student(1002,"Anita","Female",25,2234568793L,4.2,'B',true);
        System.out.println("student1: " + s1.name);
        System.out.println("student2: " + s2.name);
        System.out.println("student3: " + s3.name);

        Student[] students={s1,s2,s3};    // object array of Student type

        // Swap s1 and s3 references

        // Before Swap
        System.out.println("\n\nBefore Swap\n--------");
        System.out.println("student1: " + s1.name);
        System.out.println("student2: " + s2.name);
        System.out.println("student3: " + s3.name);

         // After swap

        swap_s1_n_s3(students,0,2);

        System.out.println("\n\nAfter Swap, Inside StudentTest class\n--------");

        System.out.println("\n\nstudent1: " + s1.name);
        System.out.println("student2: " + s2.name);
        System.out.println("student3: " + s3.name);

   }


static void swap_s1_n_s3(Student[] students,int first,int last)
   {    System.out.println("\n\n------------\nINSIDE SWAP METHOD");
        Student s5;
        s5=students[first];
        students[first]=students[last];
        students[last]=s5;
        
          System.out.println("\n\nstudent1: " + students[0].name);
        System.out.println("student2: " + students[1].name);
        System.out.println("student3: " + students[2].name);
        System.out.println("\nEXIT SWAP METHOD");

   }
 }  

OUTPUT

$ java StudentTest

student1: Joan
student2: Indresh
student3: Anita

Before Swap

student1: John
student2: Indresh
student3: Anita

INSIDE SWAP METHOD

student1: Anita
student2: Indresh
student3: John

EXIT SWAP METHOD

After Swap, Inside StudentTest class

student1: John
student2: Indresh
student3: Anita

My question is the swap funtion should also swap the references in main(), but this is not the case, why ?

The swap-logic works correctly. The problem is of a different nature.

In the code presented, the variables s1, s2 and s3 are used to hold the initial Student-objects, initialize the students-array and printed as debugging. No matter, however, what is done to and with students, these three variables reference the same Student-object that was originally assigned to them. This gets obvious when the variables are declared as final.

When printing the Students for debugging, they should be accessed through the students-array:

System.out.println("student1: " + students[0].name);
System.out.println("student2: " + students[1].name);
System.out.println("student3: " + students[2].name);

<kbd>Ideone demo</kbd>

Replace main method as below, you will get an idea.

Instead of accessing element by reference you need to access by array[index], you will get exact result what you want.

 public static void main(String args[]) {
Student s1 = new Student(1000, "John", "Male", 18, 2234567890L, 3.8, 'B');
Student s2 = new Student(1001, "Indresh", "Male", 20, 2234567893L, 4.0, 'C', true);
Student s3 = new Student(1002, "Anita", "Female", 25, 2234568793L, 4.2, 'B', true);
System.out.println("student1: " + s1.name);
System.out.println("student2: " + s2.name);
System.out.println("student3: " + s3.name);
Student[] students = {s1, s2, s3};    // object array of Student type
// Swap s1 and s3 references
// Before Swap
System.out.println("\n\nBefore Swap\n--------");
System.out.println("student1: " + s1.name);
System.out.println("student2: " + s2.name);
System.out.println("student3: " + s3.name);
// After swap
swap_s1_n_s3(students, 0, 2);
System.out.println("\n\nAfter Swap, Inside StudentTest class\n--------");
System.out.println("student1: " + students[0].name);
System.out.println("student2: " +  students[1].name);
System.out.println("student3: " +  students[2].name);
}