Custom Immutable

[Anand Surya]

Hi Team,

final class PersonImmutable {
	private final String name;
	private final Integer id;
	private final Date date;

	public PersonImmutable(String name, Integer id, Date date) {
		this.name = name;
		this.id = id;
		this.date = date;
	}

	public String getName() {
		return name;
	}

	public Integer getId() {
		return id;
	}

	public Date getDate() {
		return date;
	}
}

What is the reason that PersonImmutable class is not correct immutable class?

[Carey Brown]

Is this a homework question?

Are all members immutable?

[Campbell Ritchie]

Why have you used Integer?

[Lakshman Arun]

Because it has mutable member variables (id and date)

[Rob Spoor]

Integer (id) is not mutable.

[Santosh Kumar Nayak]

Special attention needed for  Date field

Below you can see an Immutable Class Sample :-

final class MyImmutable { 
    private final String name; 
    private  Date dob ;                                                                                  
    private List<Integer> al = new ArrayList<Integer>();

   public MyImmutable(String name, Date dob,List al) { 
       this.name = name; 
       this.dob = new Date(dob.getTime());                                                
       this.al = Collections.unmodifiableList(new ArrayList<>(al));   
   } 

   public String getName()            {   return name;   } 
   public Date getDob()  {  return new Date(dob.getTime());   } 
   public List getList() {    return al;     }

   
   public String toString(){    return name +"     "+        dob+"         "+     al ;    }  
} 


public class Immutable_Class { 
   public static void main (String args[]) { 
	   List<Integer> al = new ArrayList<Integer>();
	    al.add(7);
	    al.add(701);
	    al.add(102);
	    al.add(101);
	    
	   
	   MyImmutable imm = new MyImmutable(" Chivas regal", new Date(),al);   
       System.out.println("Old Name =" + imm.getName()); 
       String name = imm.getName(); 
       name = "George"; 
       System.out.println("New  Name =" + imm.getName());    
       
       al.add(500);
       Date dateOfBirth = imm.getDob(); 
       System.out.println("DOB" + imm.getDob());
       dateOfBirth.setTime(0); 
       System.out.println("DOB after set() called  " + dateOfBirth); 
       System.out.println("Object DOB= " + imm.getDob());
      
   } 
}

[Campbell Ritchie]

Rob Spoor wrote:Integer (id) is not mutable.

So why didn't you simply use an int?

[Rob Spoor]

The only reason I can think of is that null is allowed. The generated primary key of an entity in an ORM framework comes to mind. I'm not sure if this example qualifies though.