Java 模拟栈结构

栈和队列：

通常是作为程序猿的工具，用于辅助构思算法。生命周期较短，执行时才被创建

訪问受限。在特定时刻，仅仅有一个数据可被读取或删除

是一种抽象的结构。内部的实现机制。对用户不可见。比方用数组、链表来实现栈

栈：

同一时候，仅仅同意一个数据被訪问，后进先出

对于入栈和出栈的时间复杂度都为O(1),即不依赖栈内数据项的个数，操作比較快

例，使用数组作为栈的存储结构

public class StackS<T> {
	private int max;
	private T[] ary;
	private int top;	//指针，指向栈顶元素的下标
	
	public StackS(int size) {
		this.max = size;
		ary = (T[]) new Object[max];
		top = -1;
	}
	
	// 入栈
	public void push(T data) {
		if (!isFull())
			ary[++top] = data;
	}
	
	// 出栈
	public T pop() {
		if (isEmpty()) {
			return null;
		}
		return ary[top--];
	}
	
	// 查看栈顶
	public T peek() {
		return ary[top];
	}
	
	//栈是否为空
	public boolean isEmpty() {
		return top == -1;
	}
	
	//栈是否满
	public boolean isFull() {
		return top == max - 1;
	}
	
	//size
	public int size() {
		return top + 1;
	}
	
	public static void main(String[] args) {
		StackS<Integer> stack = new StackS<Integer>(3);
		for (int i = 0; i < 5; i++) {
			stack.push(i);
			System.out.println("size:" + stack.size());
		}
		for (int i = 0; i < 5; i++) {
			Integer peek = stack.peek();
			System.out.println("peek:" + peek);
			System.out.println("size:" + stack.size());
		}
		for (int i = 0; i < 5; i++) {
			Integer pop = stack.pop();
			System.out.println("pop:" + pop);
			System.out.println("size:" + stack.size());
		}
		
		System.out.println("----");
		
		for (int i = 5; i > 0; i--) {
			stack.push(i);
			System.out.println("size:" + stack.size());
		}
		for (int i = 5; i > 0; i--) {
			Integer peek = stack.peek();
			System.out.println("peek:" + peek);
			System.out.println("size:" + stack.size());
		}
		for (int i = 5; i > 0; i--) {
			Integer pop = stack.pop();
			System.out.println("pop:" + pop);
			System.out.println("size:" + stack.size());
		}
	}
}

上面的样例。有一个maxSize的规定。由于数组是要规定大小的，若想无限制，能够使用其它结构来做存储，当然也能够new一个新的长度的数组。

例。使用LinkedList存储来实现栈

/**
 * 使用LinkedList存储来实现栈
 * @author stone
 *
 * @param <T>
 */
public class StackSS<T> {
	private LinkedList<T> datas;
	
	public StackSS() {
		datas = new LinkedList<T>();
	}
	
	// 入栈
	public void push(T data) {
		datas.addLast(data);
	}
	
	// 出栈
	public T pop() {
		return datas.removeLast();
	}
	
	// 查看栈顶
	public T peek() {
		return datas.getLast();
	}
	
	//栈是否为空
	public boolean isEmpty() {
		return datas.isEmpty();
	}
	
	//size
	public int size() {
		return datas.size();
	}
	
	public static void main(String[] args) {
		StackS<Integer> stack = new StackS<Integer>(3);
		for (int i = 0; i < 5; i++) {
			stack.push(i);
			System.out.println("size:" + stack.size());
		}
		for (int i = 0; i < 5; i++) {
			Integer peek = stack.peek();
			System.out.println("peek:" + peek);
			System.out.println("size:" + stack.size());
		}
		for (int i = 0; i < 5; i++) {
			Integer pop = stack.pop();
			System.out.println("pop:" + pop);
			System.out.println("size:" + stack.size());
		}
		
		System.out.println("----");
		for (int i = 5; i > 0; i--) {
			stack.push(i);
			System.out.println("size:" + stack.size());
		}
		for (int i = 5; i > 0; i--) {
			Integer peek = stack.peek();
			System.out.println("peek:" + peek);
			System.out.println("size:" + stack.size());
		}
		for (int i = 5; i > 0; i--) {
			Integer pop = stack.pop();
			System.out.println("pop:" + pop);
			System.out.println("size:" + stack.size());
		}
	}
}

例，单词逆序，使用Statck结构

public class WordReverse {
	
	public static void main(String[] args) {
		reverse("株式会社");
	}
	
	static void reverse(String word) {
		if (word == null) return;
		StackSS<Character> stack = new StackSS<Character>();
		char[] charArray = word.toCharArray();
		int len = charArray.length;
		for (int i = 0; i <len; i++ ) {
			stack.push(charArray[i]);
		}
		StringBuilder sb = new StringBuilder();
		while (!stack.isEmpty()) {
			sb.append(stack.pop());
		}
		System.out.println("反转后：" + sb.toString());
	}
}

打印：

反转后：社会式株