collections

Here comes an example that stores the student object into Set and display the data in the form of key value pair.

import java.util.*;

public class Student{ 
    public static Map displayData(){
    Set<Student> set=new HashSet<Student>();
    Scanner input=new Scanner(System.in);
    for(int i=1;i<=5;i++){
    System.out.print("Enter ID: ");
    int id=input.nextInt();
    System.out.print("Enter Name: ");
    String name=input.next();

    set.add(new Student(id,name));
    }
    HashMap<Integer,String> map=new HashMap<Integer,String>();
    for(Student st:set){
       map.put(st.getStudentId(),st.getName());
    }
    return map;
    }

    private String name;
    private int studentId; 
    Student(int studentId,String name){
        this.studentId=studentId;
        this.name=name;
    }
    public void setName(String name){
        this.name=name;
    }
    public String getName(){
        return name;
    }

    public void setStudentId(int studentId){
        this.studentId=studentId;
    }
    public int getStudentId(){
        return studentId;
    }
    public static void main(String []args){
    Map map=displayData();
    Set set = map.entrySet();
    Iterator i = set.iterator();
    while(i.hasNext()) {
    Map.Entry me = (Map.Entry)i.next();
    System.out.print(me.getKey() + ": ");
    System.out.println(me.getValue());
    } 
  }
}