一月十七日星期六

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));
    }
}