传智基础与加强day05

来源：互联网发布：如何当一名网络写手编辑：程序博客网时间：2024/04/30 12:08

数组
* 定义
    * int[] arr(推荐);
    * int arr[];
* 初始化
    * int[] arr = new int[3];   事物，个体，实体（对象）
    * int[] arr = {23,34,12};
    * int[] arr = new int[]{23,34,45};

* 语法现象：
    * 数组对象会自动对数组元素做编号
       数组的下标（角标）,下标从0开始
    * 访问数组元素：
           int arr[] = new int[3];
     arr[0] = 30;
    * 获取数组的长度（元素的个数）
           属性：length
     arr.length;
        数组下标和长度之间的关系：
     maxIndex=length-1

    * 数组元素会被自动初始化为“0”值
    int[] arr = new int[3];
    arr[0]//0
    arr[1]//0
    arr[2]//0
    boolean[] arr = new boolean[3];
    arr[0]//false

    整型值：0，
    浮点：0.0,
    布尔：false,
    字符：\u0000
    String: "" " " null
    String[] str = new String[3];

*数据的定义，初始化，数组元素的访问int [] arr1=new int [3];数组对象：new int [3];数组变量：arr1数组元素：数组中具体的数据*/class  TestDemo3{public static void main(String[] args) {int []arr1=new int [3];char[]arr2=new char[3];boolean [] arr3=new boolean[3];double [] arr4=new double [3];String [] arr5=new String [3];System.out.println(arr1[0]);System.out.println(arr2[0]);System.out.println(arr3[0]);System.out.println(arr4[0]);System.out.println(arr5[0]);//数据的异常//第一种：数组下标越界异常//java.lang.ArrayIndexOUtOfBoundsExceptionSystem.out.println(arr1[3]);//arr1[3] 超出范围  int [] arr=null;//第二种：空指针异常//java.lang.NullPointerExceptiontest(arr);//数值为null(javac编译没有错误，在解析时出错。}public static void test(int [] arr){System.out.println(arr[2]);}}

数组的三种遍历

/*数组的遍历（两种*/import java.util.*;class BianLi {public static void main(String[] args){String [] names={"王世充", "李渊", "杨坚", "郭树清", "李鸿忠", "王穗明","刘铁男", "李登辉", "彭长健", "邓鸿", "王中军", "景百孚", "赵永亮", "陆兆禧", "严介和" ,"郁亮", "茅于轼", "王小波", "冯唐", "马未都" };for (int i=0;i<names.length ;i++ ){System.out.print(names[i]+" ");//第一种}System.out.println("===========================================================");for (String name:names){System.out.print(name+" ");}//第二种System.out.println("===========================================================");System.out.print(Arrays.toString(names));//第三种}}

洗牌

/*一副扑克牌，washCard洗牌*/import java.util.*;class WashCard{public static void main(String[] args) {String [] card= {"大王","小王","红桃A","红桃K","红桃Q","红桃J","红桃10","红桃9"};washCard(card);System.out.println(Arrays.toString(card));}public static void washCard(String [] card){   Random r =new Random();                for (int i=0;i<card.length ;i++ ){int n=r.nextInt(card.length); String trans=null;           trans=card[i];card[i]=card[n];card[n]=trans;}}}

双色球

/*机选双色球：{"01", "02", "03",  "04","05","06","07","08","09","10",~33}{false,true,false,false....}*/import java.util.*;class Demo07 {public static void main(String[] args) {String[] redBalls = getBalls();System.out.println(Arrays.toString(redBalls));}/*定义方法返回值类型：String[]参数：无*/public static String[] getBalls(){String[] pool = {"01", "02", "03",  "04","05","06","07","08","09","10",    "11", "12", "13",  "14","15","16","17","18","19","20",    "21", "22", "23",  "24","25","26","27","28","29","30","31", "32", "33"};boolean[] flags = new boolean[33];String[] balls = new String[7];Random r = new Random();int i = 0;for(;;){int index = r.nextInt(pool.length);if(!flags[index]){//flags == falseballs[i] = pool[index];i++;flags[index] = true;}if(i==6){break;}}int blueIndex = r.nextInt(16);balls[6] = pool[blueIndex];System.out.println(balls[6]);//对数组的排序Arrays.sort(balls,0,5);return balls;}}

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