Difference between pop () and peek () in stack

Java.util.Stack pop () and peek () operation check memo

There was no blog about behavior confirmation, so a memo.

Below you can see what you can see on the API.

public E pop()

Removes the first object on the stack and returns that object as the value of the function Return value: The object at the top of the stack (the last item in the Vector object). Exception: EmptyStackException-if this stack is empty (https://docs.oracle.com/javase/jp/8/docs/api/java/util/Stack.html#pop--)

public E peek()

Fetch the object at the top of the stack. The object is not removed from the stack at this time. Return value: The object at the top of the stack (the last item in the Vector object). Exception: EmptyStackException-if this stack is empty (https://docs.oracle.com/javase/jp/8/docs/api/java/util/Stack.html#peek--)

For peek.java


public static void main(String[] args) {
  try {
    Stack<String> stack = new Stack();
    stack.push("Good Morning!");
    stack.push("Hello!");
    stack.peek();
    stack.stream().forEach(System.out::println);
    // Good Morning!
    // Hello!
  } catch (EmptyStackException e) {
    System.out.println("stack is empty");
  }
}

In the case of pop.java


public static void main(String[] args) {
  try {
    Stack<String> stack = new Stack();
    stack.push("Good Morning!");
    stack.push("Hello!");
    stack.pop();
    stack.stream().forEach(System.out::println);
    // Good Morning!
  } catch (EmptyStackException e) {
    System.out.println("stack is empty");
  }
}

If pop, it is pushed from the stack, and peek is not pushed from the stack. If you look at peek's API, it will return a return value, so you can pop while verifying the value.

Pop while verifying.java


public static void main(String[] args) {
  try {
    Stack<String> stack = new Stack();
    stack.push("Good Morning!");
    stack.push("Hello!");
    if (stack.peek().equals("Hello!")) {
      stack.pop();
    }
    System.out.println(stack.peek());
    // Good Morning!
  } catch (EmptyStackException e) {
    System.out.println("stack is empty");
  }
}

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