abstractor method with object return type in java

I'm new at oop ,I want to pass object parameter of an abstract method but it gives me error, can anyone explain it to me and help me fix the error . Thanks for your help.

abstract class FunctionInt{
int num1;
int num2;

abstract FunctionInt test(FunctionInt newNum);

}

class Function extends FunctionInt{
public Function(int num1,int num2){
this.num1=num1;
this.num2=num2;
}
public Function (){

}

Function test(Function c){
return c;
}

You cannot change the abstract method signature. You have created an entirely new method unrelated to the method you wanted to override. Use the @Override annotation to spot this class of errors more quickly.

public class Function extends FunctionInt {
    public Function(int num1, int num2) {
        this.num1 = num1;
        this.num2 = num2;
    }

    public Function() {

    }

    @Override
    FunctionInt test(FunctionInt c) {
        return c;
    }
}