Java uses the peek() function of the Stack class to get the top element in the stack

Java uses the peek() function of the Stack class to obtain the top element in the stack

In Java programming, the stack (Stack) is a commonly used data structure, which follows the first-in, last-out (Last-In -First-Out, LIFO) principle. In Java, we can use the Stack class to implement stack operations, where the peek() function is the method used to get the top element in the stack.

Before using the Stack class, we first need to import the java.util package in order to use the Stack class in it.

import java.util.Stack;

Next, we can create a Stack object and use the push() method to insert elements into the stack.

Stack<String> stack = new Stack<>();

stack.push("元素1");
stack.push("元素2");
stack.push("元素3");

Now, we have three elements in our stack, namely "Element 1", "Element 2" and "Element 3". We can use the peek() method to get the top element of the stack.

String topElement = stack.peek();
System.out.println("堆栈的顶部元素是：" + topElement);

Run the above code, the output should be: "The top element of the stack is: element 3". The reason is that the last element we inserted was "element 3", so it is at the top of the stack.

It should be noted that the peek() method is only used to obtain the top element of the stack and does not remove it from the stack. If we want to get the top element of the stack and remove it from the stack at the same time, we can use the pop() method.

String topElement = stack.pop();
System.out.println("堆栈的顶部元素是：" + topElement);

Run the above code, the output result is also: "The top element of the stack is: element 3", but at this time, there is no "element 3" in the stack.

Sometimes, we may determine whether the stack is empty before using the peek() method. We can use the isEmpty() method to achieve this.

if (!stack.isEmpty()) {
    String topElement = stack.peek();
    System.out.println("堆栈的顶部元素是：" + topElement);
} else {
    System.out.println("堆栈为空！");
}

The above code first determines whether the stack is empty. If it is not empty, use the peek() method to obtain the top element of the stack. If the stack is empty, the prompt message "Stack is empty!" is output.

Summary:

• Stack operations can be implemented using the Stack class.
• Thepeek() method is used to get the top element of the stack.
• Thepeek() method does not remove the top element of the stack from the stack.
• Use the pop() method to obtain and remove the top element of the stack at the same time.
• Use the isEmpty() method to determine whether the stack is empty.

The stack is one of the common data structures in Java programming. When processing some data that needs to be operated in a first-in, last-out manner, using the stack can be more convenient and efficient. With the peek() method, we can easily get the top element of the stack without changing the contents of the stack.

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