- [0.0.1. 泛型的实际应用:实现最小值函数](#001-%e6%b3%9b%e5%9e%8b%e7%9a%84%e5%ae%9e%e9%99%85%e5%ba%94%e7%94%a8%e5%ae%9e%e7%8e%b0%e6%9c%80%e5%b0%8f%e5%80%bc%e5%87%bd%e6%95%b0) - [0.0.2. 使用数组实现栈](#002-%e4%bd%bf%e7%94%a8%e6%95%b0%e7%bb%84%e5%ae%9e%e7%8e%b0%e6%a0%88) - [0.0.3. 实现线程安全的 LRU 缓存](#003-%e5%ae%9e%e7%8e%b0%e7%ba%bf%e7%a8%8b%e5%ae%89%e5%85%a8%e7%9a%84-lru-%e7%bc%93%e5%ad%98) ### 0.0.1. 泛型的实际应用:实现最小值函数 自己设计一个泛型的获取数组最小值的函数.并且这个方法只能接受Number的子类并且实现了Comparable接口。 ```java //注意：Number并没有实现Comparable private static > T min(T[] values) { if (values == null || values.length == 0) return null; T min = values[0]; for (int i = 1; i < values.length; i++) { if (min.compareTo(values[i]) > 0) min = values[i]; } return min; } ``` 测试： ```java int minInteger = min(new Integer[]{1, 2, 3});//result:1 double minDouble = min(new Double[]{1.2, 2.2, -1d});//result:-1d String typeError = min(new String[]{"1","3"});//报错 ``` ### 0.0.2. 使用数组实现栈 **自己实现一个栈，要求这个栈具有`push()`、`pop()`（返回栈顶元素并出栈）、`peek()` （返回栈顶元素不出栈）、`isEmpty()`、`size()`这些基本的方法。** 提示：每次入栈之前先判断栈的容量是否够用，如果不够用就用`Arrays.copyOf()`进行扩容； ```java public class MyStack { private int[] storage;//存放栈中元素的数组 private int capacity;//栈的容量 private int count;//栈中元素数量 private static final int GROW_FACTOR = 2; //不带初始容量的构造方法。默认容量为8 public MyStack() { this.capacity = 8; this.storage=new int[8]; this.count = 0; } //带初始容量的构造方法 public MyStack(int initialCapacity) { if (initialCapacity < 1) throw new IllegalArgumentException("Capacity too small."); this.capacity = initialCapacity; this.storage = new int[initialCapacity]; this.count = 0; } //入栈 public void push(int value) { if (count == capacity) { ensureCapacity(); } storage[count++] = value; } //确保容量大小 private void ensureCapacity() { int newCapacity = capacity * GROW_FACTOR; storage = Arrays.copyOf(storage, newCapacity); capacity = newCapacity; } //返回栈顶元素并出栈 private int pop() { if (count == 0) throw new IllegalArgumentException("Stack is empty."); count--; return storage[count]; } //返回栈顶元素不出栈 private int peek() { if (count == 0){ throw new IllegalArgumentException("Stack is empty."); }else { return storage[count-1]; } } //判断栈是否为空 private boolean isEmpty() { return count == 0; } //返回栈中元素的个数 private int size() { return count; } } ``` 验证 ```java MyStack myStack = new MyStack(3); myStack.push(1); myStack.push(2); myStack.push(3); myStack.push(4); myStack.push(5); myStack.push(6); myStack.push(7); myStack.push(8); System.out.println(myStack.peek());//8 System.out.println(myStack.size());//8 for (int i = 0; i < 8; i++) { System.out.println(myStack.pop()); } System.out.println(myStack.isEmpty());//true myStack.pop();//报错：java.lang.IllegalArgumentException: Stack is empty. ```