Stack是后进先出 (LIFO) 数据结构。它支持两种基本操作，称为push 和pop。 push 操作在栈顶添加一个元素，pop 操作从栈顶移除一个元素。

Java 提供了一个 Stack 类，它对 Stack 数据结构进行建模。 Stack 类是 Java 集合框架的一部分。以下是 Java 中 Stack 的类层次结构 -

Stack 类扩展了 Vector，它实现了 List 接口。 Vector 是一个可重新调整大小的集合。它会增大其大小以容纳新元素，并在删除元素时缩小其大小。

由于 Stack 类扩展了 Vector，当添加或删除新元素时，它也会根据需要增加和缩小其大小。

创建Stack并执行基本操作，如推送、弹出和查看

import java.util.Stack;

public class StackExample {
    public static void main(String[] args) {
        // Creating a Stack
        Stack<String> stackOfCards = new Stack<>();

        // Pushing new items to the Stack
        stackOfCards.push("Jack");
        stackOfCards.push("Queen");
        stackOfCards.push("King");
        stackOfCards.push("Ace");

        System.out.println("Stack => " + stackOfCards);
        System.out.println();

        // Popping items from the Stack
        String cardAtTop = stackOfCards.pop();  // Throws EmptyStackException if the stack is empty
        System.out.println("Stack.pop() => " + cardAtTop);
        System.out.println("Current Stack => " + stackOfCards);
        System.out.println();

        // Get the item at the top of the stack without removing it
        cardAtTop = stackOfCards.peek();
        System.out.println("Stack.peek() => " + cardAtTop);
        System.out.println("Current Stack => " + stackOfCards);

    }
}

# Output
Stack => [Jack, Queen, King, Ace]

Stack.pop() => Ace
Current Stack => [Jack, Queen, King]

Stack.peek() => King
Current Stack => [Jack, Queen, King]

其他Stack操作

• 检查栈是否为空。
• 求栈的大小。
• 在Stack中搜索一个元素。

import java.util.Stack;

public class StackSizeSearchExample {
    public static void main(String[] args) {
        Stack<String> stackOfCards = new Stack<>();

        stackOfCards.push("Jack");
        stackOfCards.push("Queen");
        stackOfCards.push("King");
        stackOfCards.push("Ace");

        System.out.println("Stack : " + stackOfCards);

        // Check if the Stack is empty
        System.out.println("Is Stack empty? : " + stackOfCards.isEmpty());

        // Find the size of Stack
        System.out.println("Size of Stack : " + stackOfCards.size());

        // Search for an element
        // The search() method returns the 1-based position of the element from the top of the stack
        // It returns -1 if the element was not found in the stack
        int position = stackOfCards.search("Queen");

        if(position != -1) {
            System.out.println("Found the element \"Queen\" at position : " + position);
        } else {
            System.out.println("Element not found");
        }

    }
}

# Output
Stack : [Jack, Queen, King, Ace]
Is Stack empty? : false
Size of Stack : 4
Found the element "Queen" at position : 3

迭代Stack

本节中的示例展示了迭代 Stack 的各种方法。

• 使用 Java 8 forEach() 迭代Stack。
• 使用 iterator() 迭代Stack。
• 使用 iterator() 和 Java 8 forEachRemaining() 方法迭代Stack。
• 使用 listIterator() 从上到下迭代Stack。

import java.util.Iterator;
import java.util.ListIterator;
import java.util.Stack;

public class IterateOverStackExample {
    public static void main(String[] args) {
        Stack<String> stackOfPlates = new Stack<>();

        stackOfPlates.add("Plate 1");
        stackOfPlates.add("Plate 2");
        stackOfPlates.add("Plate 3");
        stackOfPlates.add("Plate 4");

        System.out.println("=== Iterate over a Stack using Java 8 forEach() method ===");
        stackOfPlates.forEach(plate -> {
            System.out.println(plate);
        });

        System.out.println("\n=== Iterate over a Stack using iterator() ===");
        Iterator<String> platesIterator = stackOfPlates.iterator();
        while (platesIterator.hasNext()) {
            String plate = platesIterator.next();
            System.out.println(plate);
        }

        System.out.println("\n=== Iterate over a Stack using iterator() and Java 8 forEachRemaining() method ===");
        platesIterator = stackOfPlates.iterator();
        platesIterator.forEachRemaining(plate -> {
            System.out.println(plate);
        });

        System.out.println("\n=== Iterate over a Stack from TOP to BOTTOM using listIterator() ===");
        // ListIterator allows you to traverse in both forward and backward directions.
        // We'll start from the top of the stack and traverse backwards.
        ListIterator<String> platesListIterator = stackOfPlates.listIterator(stackOfPlates.size());
        while (platesListIterator.hasPrevious()) {
            String plate = platesListIterator.previous();
            System.out.println(plate);
        }
    }
}

# Output
=== Iterate over a Stack using Java 8 forEach() method ===
Plate 1
Plate 2
Plate 3
Plate 4

=== Iterate over a Stack using iterator() ===
Plate 1
Plate 2
Plate 3
Plate 4

=== Iterate over a Stack using iterator() and Java 8 forEachRemaining() method ===
Plate 1
Plate 2
Plate 3
Plate 4

=== Iterate over a Stack from TOP to BOTTOM using listIterator() ===
Plate 4
Plate 3
Plate 2
Plate 1

结论

在本文中，您了解了什么是 Stack，如何在 Java 中创建 Stack，如何在 Stack 中执行 push 和 pop 操作，如何检查 Stack 是否为空，如何找到 Stack 的大小以及如何搜索Stack中的元素。