Assigning in Java?

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Yes, it does – but the value of A is a reference, not a copy of the object itself.

I like to give the following analogy…

Suppose two people both have my address: that’s like two variables of type House in Java. Now one of them comes and paints my door red. The second person will still see the red door if they visit:

House jonsHouse = new House(); // Even the variable jonsHouse is only a reference

House firstAddressCopy = jonsHouse; // Just a copy of the reference
House secondAddressCopy = jonsHouse; // Just a copy of the reference

firstAddressCopy.paintDoor(Color.Red);

Color color = secondAddressCopy.getDoorColor(); // Now color will be red

Basically, remember a few rules and things will become clear:

  • The value of an expression in Java is never an object – only ever a reference or a primitive value
  • (Corollary of first point) A variable never holds an object – only ever a reference or a primitive value
  • Assignment (and argument passing) always copies the value, whether that value is a reference or a primitive value

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