very basic java method

Question

I am a beginner in java and am writing a stack class using array.

So I have a method in this class called pop

 public int Pop(){
 if (current_size >0)
 { // do something 
 return ele;
 }
 // return nothing <-- ths is where error is
 }

Since i have the return type int.. the class is always expecting to return something. How should I tackle such cases where the method wil return something if the condition is true else it wont shouldnt return anything? Thanks

• Makoto: There's....a lot wrong here. First, where is your array? You're not using it in this method. Second, it's difficult to decide what to return when the stack is empty, since any primitive int may be a valid entry in the stack. Third, I don't see anything that reduces the size of the stack or adjusts where the end of the stack is pointing to.

Answer 1

You must always return something (unless your method is void) or throw an exception. You could try this:

public int pop() {
 if (current_size > 0) 
 return ele;
 throw new EmptyStackException();
}

Answer 2

Without knowing what your desired behavior is, it is hard to tell you, but I can provide a couple suggestions.

1. If you want to truly return nothing, you should change the return type to be the Integer wrapper class rather than the int primitive. This way you can return null which would be nothing.

2. If this is an exceptional case, perhaps you want to throw an Exception.

   if (evaluateSomething()) {
    // do something in response...
   } else {
    throw new RuntimeException("You can't do that!");
   }
   

Answer 3

You could raise an exception when the stack is empty, or you could return a special int like -1 if your stack never has negative numbers.

throw new StackIsEmptyException();

Answer 4

You need to have a return statement or throw an exception for all possible exit point.

Answer 5

Unless your method is void, you must either return a variable or throw/catch an exception. Something like this should do;

 public int pop() 
{
 if (current_size > 0) 
 return ele; //return variable
 throw new EmptyStackException(); //throw new exception
}