Java 基础(Arrays工具类的使用, 数组中的常见异常)

java.util.Arrays类即为操作数组的工具类，包含了用来操作数组(比如搜索和排序)的各种方法

序号	方法	说明
1	boolean equals(int[] a, int[] b)	判断连个数组是否相等
2	String toString(Int[] a)	输出数组的信息
3	void fill(int[] a, int val)	将指定值填充到数组之中
4	void sort(int[] a)	对数组进行排序
5	int binarySearch(int[] a, int key)	对排序后的数组进行二分法检索指定的值

import java.util.Arrays;

public class ArraysTest {
	public static void main(String[] args) {
		//1.判断两个数组是否相等
		int[] arr1 = new int[]{1, 2, 3, 4};
		int[] arr2 = new int[]{1, 3, 2, 4};
		boolean isEquals = Arrays.equals(arr1, arr2);
		System.out.println(isEquals);    //false
		
		//2.输出数组的信息
		System.out.println(Arrays.toString(arr1));
		
		//3.把指定的值填充到数组之中
		Arrays.fill(arr1, 10);
		System.out.println(Arrays.toString(arr1));
		
		//4.对数组进行排序
		Arrays.sort(arr2);
		System.out.println(Arrays.toString(arr2));
		
		//5.二分法查找
		int[] arr3 = new int[] {-98, -34, 2, 34, 54, 78, 79, 106, 210, 333};
		int index = Arrays.binarySearch(arr3, 210);
		if(index >= 0) {
			System.out.println(index);
		}else {
			System.out.println("未找到~");
		}
		
	}

}

数组中的常见异常

1. 数组角标越界异常：ArrayIndexOutOfBoundsException

public class ArrayExecptionTest {
	public static void main(String[] args){
		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]);   //同样报错         
	}

}

2.空指针异常: NullPointerException

public class ArrayExecptionTest {
	public static void main(String[] args){
		//情况一：
		//int[] arr1 = new int[]{1, 2, 3};
		//arr1 = null;
		//System.out.println(arr1[0]); //Exception in thread "main" java.lang.NullPointerException: Cannot load from int array because "arr1" is null

                //情况二：
		//int[][] arr2 = new int[4][];
		//System.out.println(arr2[0][0]);  //Exception in thread "main" java.lang.NullPointerException: Cannot load from int array because "arr2[0]" is null
                  
                //情况三:
		String[] arr3 = new String[]{"AA", "BB", "CC"};
		arr3[0] = null;
		System.out.println(arr3[0].toString()); //Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.toString()" because "arr3[0]" is null

	}

}