Java基本语法3-快速排序、Arrays工具类、数组常见异常

代码实现：

    public static void swap(int[] data,int i,int j){
        int temp = data[i];
        data[i] = data[j];
        data[j] = temp;
    }
    public static void subSort(int[] data,int start,int end){
        if(start < end){
            int base = data[start];
            int low = start;
            int high = end + 1;
            while(true){
                while (low< end && data[++low]-base<=0); //先看左边，low比base小的话就递加
                while (high > start && data[--high] - base>=0); //再看右边，high比base大的话就递减
                if (low 
数组中常见算法性能对比 
 
Arrays工具类的使用 
int arr1[] = new int[] { 21, 43, 542, 432, 4, 2, 5, 1 };
int arr2[] = new int[] { 32, 43, 4, 1, 4, 76, 54, 68, 4 };

// 1.Arrays.equals(arr1, arr2):判断数组是否相等
System.out.println(Arrays.equals(arr1, arr2));
// 2.Arrays.toString(arr1):输出数组信息
System.out.println(Arrays.toString(arr1));

// 3.Arrays.fill(arr1, 2):将指定值填充到数组中
Arrays.fill(arr1, 2);
System.out.println(Arrays.toString(arr1));
// 4.Arrays.sort(arr2):对数组进行排序
Arrays.sort(arr2);
System.out.println(Arrays.toString(arr2));
// 5.Arrays.binarySearch(arr2, 1):堆排序好的数组用二分法检索指定值
int index = Arrays.binarySearch(arr2, 1);
System.out.println(index);


 
运行结果：
 false
 [21, 43, 542, 432, 4, 2, 5, 1]
 [2, 2, 2, 2, 2, 2, 2, 2]
 [1, 4, 4, 4, 32, 43, 54, 68, 76]
 0
 
数组中常见的异常 
1.数组角标越界异常： 
int[] arr = new int[]{1,2,3,4,5};

for(int i = 0;i <= arr.length;i++){
    System.out.println(arr[i]);
}

System.out.println(arr[-2]);

System.out.println("hello");


 
结果：
 
1
2
3
4
5
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5
	at helloworld.main(helloworld.java:194)
 
2.空指针异常： 
//情况一：
int[] arr1 = new int[]{1,2,3};
arr1 = null;
System.out.println(arr1[0]);

//情况二：
int[][] arr2 = new int[4][];
System.out.println(arr2[0][0]);

//情况：
String[] arr3 = new String[]{"AA","BB","CC"};
arr3[0] = null;
System.out.println(arr3[0].toString());

 
结果
 
Exception in thread "main" java.lang.NullPointerException: Cannot load from int array because "arr1" is null
	at helloworld.main(helloworld.java:194)