java - passing a double value by reference

Question

how can I pass a double value by reference in java?

example:

Double a = 3.0;
Double b = a;
System.out.println(\"a: \"+a+\" b: \"+b);
a = 5.0;
System.         


        

Answer 1

Double is immutable in Java. The assignment a = 5.0 is not changing the Double value of a. It is actually creating an entirely new Double object and changing the value of the pointer that a holds to point at that new object. If you want to be able to change the value without changing the reference, you need to make a mutable Double.

public class MutableDouble {
  private Double value;

  public Double getValue() {
    return value;
  }

  public void setValue(Double value) {
    this.value = value;
  }

  @Override
  public String toString() {
    return value != null ? value.toString() : "null";
  }
}

Then you would call a.setValue(5.0); and both would change.