栈和队列：
一般是作为程序员的工具，用于辅助构思算法，生命周期较短，运行时才被创建
访问受限，在特定时刻，只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，比如用数组、链表来实现栈
栈：
同时，只允许一个数据被访问，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，操作比较快
例，使用数组作为栈的存储结构
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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()

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());
}
}
}

上面的例子，有一个maxSize的规定，因为数组是要规定大小的，若想无限制，可以使用其他结构来做存储，当然也可以new一个新的长度的数组。
例，使用LinkedList存储来实现栈
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/**
* 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());
}
}
}