Java – if the return type of the rewriting method is original (such as double), can we change the return type of the rewriting method (such as int, char)?

• Java

As follows:

Method to override:

double add (int a,int b){  

}

Method of covering the above method:

int add(int a,int b){

}

Solution

It is impossible to use primitive types, but JDK 1.5 adds a function called covariant return types Therefore, with this function, a subclass can return a more specific type than the type declared by the parent class

The following code compiles well in JDK 1.7

public static class A {
   Number go() { return 0; };
}

public static class B extends A {
  @Override
  Integer go() { return 0; }
}

See JLS example 8.4 8.3-1. Covariant Return Types

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