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125 lines
3.2 KiB
Markdown
125 lines
3.2 KiB
Markdown
## 泛型的实际应用
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### 实现最小值函数
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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。
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```java
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//注意：Number并没有实现Comparable
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private static <T extends Number & Comparable<? super T>> T min(T[] values) {
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if (values == null || values.length == 0) return null;
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T min = values[0];
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for (int i = 1; i < values.length; i++) {
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if (min.compareTo(values[i]) > 0) min = values[i];
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}
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return min;
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}
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```
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测试：
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```java
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int minInteger = min(new Integer[]{1, 2, 3});//result:1
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double minDouble = min(new Double[]{1.2, 2.2, -1d});//result:-1d
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String typeError = min(new String[]{"1","3"});//报错
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```
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## 数据结构
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### 使用数组实现栈
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**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。**
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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；
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```java
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public class MyStack {
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private int[] storage;//存放栈中元素的数组
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private int capacity;//栈的容量
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private int count;//栈中元素数量
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private static final int GROW_FACTOR = 2;
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//TODO：不带初始容量的构造方法。默认容量为8
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public MyStack() {
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this.capacity = 8;
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this.storage=new int[8];
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this.count = 0;
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}
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//TODO：带初始容量的构造方法
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public MyStack(int initialCapacity) {
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if (initialCapacity < 1)
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throw new IllegalArgumentException("Capacity too small.");
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this.capacity = initialCapacity;
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this.storage = new int[initialCapacity];
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this.count = 0;
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}
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//TODO：入栈
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public void push(int value) {
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if (count == capacity) {
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ensureCapacity();
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}
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storage[count++] = value;
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}
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//TODO：确保容量大小
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private void ensureCapacity() {
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int newCapacity = capacity * GROW_FACTOR;
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storage = Arrays.copyOf(storage, newCapacity);
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capacity = newCapacity;
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}
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//TODO：返回栈顶元素并出栈
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private int pop() {
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count--;
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if (count == -1)
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throw new IllegalArgumentException("Stack is empty.");
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return storage[count];
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}
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//TODO：返回栈顶元素不出栈
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private int peek() {
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if (count == 0){
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throw new IllegalArgumentException("Stack is empty.");
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}else {
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return storage[count-1];
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}
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}
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//TODO：判断栈是否为空
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private boolean isEmpty() {
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return count == 0;
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}
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//TODO：返回栈中元素的个数
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private int size() {
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return count;
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}
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}
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```
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验证
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```java
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MyStack myStack = new MyStack(3);
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myStack.push(1);
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myStack.push(2);
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myStack.push(3);
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myStack.push(4);
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myStack.push(5);
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myStack.push(6);
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myStack.push(7);
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myStack.push(8);
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System.out.println(myStack.peek());//8
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System.out.println(myStack.size());//8
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for (int i = 0; i < 8; i++) {
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System.out.println(myStack.pop());
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}
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System.out.println(myStack.isEmpty());//true
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myStack.pop();//报错：java.lang.IllegalArgumentException: Stack is empty.
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``` |