Java程序设计题
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 extends Number & Comparable<? super T>> 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
数据结构
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;
//TODO：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;
}
//TODO：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;
}
//TODO：入栈
public void push(int value) {
if (count == capacity) {
ensureCapacity();
}
storage[count++] = value;
}
//TODO：确保容量大小
private void ensureCapacity() {
int newCapacity = capacity * GROW_FACTOR;
storage = Arrays.copyOf(storage, newCapacity);
capacity = newCapacity;
}
//TODO：返回栈顶元素并出栈
private int pop() {
count--;
if (count == -1)
throw new IllegalArgumentException("Stack is empty.");
return storage[count];
}
//TODO：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];
}
}
//TODO：判断栈是否为空
private boolean isEmpty() {
return count == 0;
}
//TODO：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.
