Duplicating objects in Java

by

Every variable in Java is a reference. So when you do

SomeClass s2 = s1;

you just point s2 to the same object as s1 points to. You are actually assigning the value of the reference s1 (which points to an instance of SomeClass) to s2. If you modify s1, s2 will be modified as well (because it points to the same object).

There is an exception, primitive types: int, double, float, boolean, char, byte, short, long. They are stored by value. So when using =, you only assign the value, but they can not point to the same object (because they are not references). This means that 

int b = a;

only sets the value of b to the value of a. If you change a, b will not change.

At the end of the day, everything is assignment by value, it’s just the value of the reference and not the value of the object (with the exception of primitive types as mentioned above).

So in your case, if you want to make a copy of s1, you can do it like this:

SomeClass s1 = new SomeClass("first");
SomeClass s2 = new SomeClass(s1.getText());

Alternatively, you can add a copy constructor to SomeClass that takes an instance as argument and copies it into its own instance.

class SomeClass {
  private String text;
  // all your fields and methods go here

  public SomeClass(SomeClass copyInstance) {
    this.text = new String(copyInstance.text);
  }
}

With this you can copy an object pretty easily:

SomeClass s2 = new SomeClass(s1);

More Related Contents:

  1. What is the difference between a variable, object, and reference? [duplicate]
  2. the difference between reference and object in java [duplicate]
  3. What are classes, references, and objects?
  4. Creating a variable name using a String value
  5. What exactly is an instance in Java?
  6. What is difference between references and objects in java? [duplicate]
  7. Java String variable setting – reference or value?
  8. Is it possible see all the references to an object in execution time?
  9. Same thing like C++ pointer in Java
  10. Java new keyword
  11. Difference between Object[] and Array of specific Objects in java
  12. How to pass an object from one activity to another on Android
  13. How do I copy an object in Java?
  14. Java Serializable Object to Byte Array
  15. The difference between Classes, Objects, and Instances
  16. What is an object’s hash code if hashCode() is not overridden?
  17. Function Pointers in Java
  18. Environment variables in Eclipse
  19. Java: difference between strong/soft/weak/phantom reference
  20. Why is the toString() method being called when I print an object?
  21. Java, pass-by-value, reference variables
  22. How to cast an Object to an int
  23. java StackOverflowError when local and instance objects creation
  24. Inheritance in java and Superclasses(Object, Class)
  25. How default .equals and .hashCode will work for my classes?
  26. What is the use of a private static variable in Java?
  27. Convert String into a Class Object [closed]
  28. How can I turn a JSONArray into a JSONObject?
  29. Using Gson and Abstract Classes
  30. Does Java autobox when assigning an int to an Object?

Leave a Comment