此代码中Integer.Min_value的用途是什么？

Question

What is the use of Integer.Min_value in this code? I know it is dereference S[top] for garbage collection, but need to know more about it

public int pop() throws Exception {

    int data;
    if (isEmpty())
        throw new Exception("Stack is empty.");
    data = S[top];
    S[top--] = Integer.MIN_VALUE; 
    return data;
} 

Answer 1

Imagine you have a stack defined as an array such as this:

S = [ 1, 2, 3, 4, 5 ]

Stacks are last in, first out. The top variable should always be the index of the "last in" stack item, in this case top = 4 because the last number in is 5 and has an index of 4 .

What this does is assign the content of S[top] to data , then assign Integer.MIN_VALUE to S[top] to "clear" it, and then decrease top by 1.

This line: S[top--] = Integer.MIN_VALUE; can be rewritten as the following:

S[top] = Integer.MIN_VALUE; top = top - 1;

I think that the end goal is to clear old values in the stack and give them a default without having to resize the array.

Once the pop method has been executed, here's the result: S: [ 1, 2, 3, 4, -2147483648 ] and top: 3 and the "last in" item in the stack will be 4 .

Hope this makes sense.