import java.util.Arrays;public class ArrayTest3 {    public static void main(String[] args) {        Test3 Test3Object = new Test3();//        System.out.println(t1.x);        System.out.println("arr1:"+Arrays.toString(Test3Object.arr1));//        t1.arr1[0]=1;//Exception in thread "main" java.lang.NullPointerException:空指针异常        System.out.println("arr2:"+Arrays.toString(Test3Object.arr2));        System.out.println("arr3:"+Arrays.toString(Test3Object.arr3));        System.out.println("length arr3:"+Test3Object.arr3.length);//        t1.arr3[0]=1;//Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0        System.out.println("arr4:"+Arrays.toString(Test3Object.arr4));        System.out.println("arr5:"+Arrays.toString(Test3Object.arr5));    }}class Test3 {    int[] arr1;//声明了一个数组变量,为引用类型.没有初始化,即没有引用数组对象.    //创建数组对象一旦创建(new)所有元素初始化为默认值.    int[] arr2=new int[1];//0    int[] arr3={};//长度为0的数组,与null不同    String[] arr4=new String[1];//null    boolean[] arr5=new boolean[1];//false    int x;    void array() {        // int[] array;        // System.out.println(Arrays.toString(array));//Exception in thread        // "main" java.lang.Error: 局部变量没有初始化    }}

import java.util.Arrays;public class sort {    public static void BubbleSort(int[] array){        for(int x=0;x<array.length-1;x++){            for(int y=0;y<array.length-1-x;y++){                if (array[y]>array[y+1]) {                    int temp=array[y+1];                    array[y+1]=array[y];                    array[y]=temp;                }            }        }    }    public static void InsertSort(int[] array) {        for (int i = 1; i < array.length; i++) {            for (int j = i; (j > 0) && (array[j] < array[j - 1]); j--) {                swap(array, j, j-1 );            }        }    }    public static void swap(int[] data,int a,int b) {        int temp=data[a];        data[a]=data[b];        data[b]=temp;    }    public static void main(String[] args) {        int[] arr={5,4,3,2,1};        System.out.println("array:"+Arrays.toString(arr));//        BubbleSort(arr);        InsertSort(arr);        System.out.println("after sort:"+Arrays.toString(arr));    }}