JAVA数组以及小练习

目录

数组的概述和静态初始化

数组的地址值和元素访问

数组的遍历

数组的动态初始化

数组练习

数组的概述和静态初始化

---

package 数组;

public class array1 {
    public static void main(String[] args){
        //格式
        //静态初始化
        //数据类型 [] 数组名 = new 数组类型[]{元素1，元素2}

        //姓名
        String [] name1 = new String[]{"12","13","14"};
        String [] name2 = {"12","13","14"};

        //年龄
        int [] age1 = new int[]{20,21,22};
        int [] age2 = {20,21,22};

        //身高
        double [] cm1 = new double[]{1.78,1.55,1.20};
        double [] cm2 = {1.78,1.55,1.20};
    }
}

---

数组的地址值和元素访问

package 数组;

public class array2 {
    public static void main(String[] args){
        //格式
        //静态初始化
        //数据类型 [] 数组名 = new 数组类型[]{元素1，元素2}

        //姓名
        String [] name1 = new String[]{"12","13","14"};
        String [] name2 = {"12","13","14"};

        //年龄
        int [] age1 = new int[]{20,21,22};
        int [] age2 = {20,21,22};

        //身高
        double [] cm1 = new double[]{1.78,1.55,1.20};
        double [] cm2 = {1.78,1.55,1.20};

        String number1 = name1[0];
        int number2 = age1[0];
        double number3 = cm1[0];

        System.out.println("我叫" + number1 + "!");
        System.out.println("今年" + number2 + "岁!");
        System.out.println("我的身高是" + number3 + "m!");

        System.out.println(name1[1]);

        age1[0] = 121;
        System.out.println(age1[0]);
    }
}

---

数组的遍历

package 数组;

import sun.security.util.Length;

public class arraylx1 {
    public static void main(String[] args){
        /* 定义一个数组，存储1,2,3,4,5,6,7,8,9,10遍历数组得到每一个元素。
要求:
1，如果是奇数，则将当前数字扩大两倍
2，如果是偶数，则将当前数字变成二分之一
*/

        int number[] = {1,2,3,4,5,6,7,8,9,10};

        for (int i  =0 ; i < number.length ; i++){
            if (number[i] % 2 == 0){
                number[i] = number[i] / 2;
            }else{
                number[i] = number[i] * 2;
            }
        }
        for (int i = 0 ; i < number.length; i++){
            System.out.println(number[i]);
        }
    }
}

---

数组的动态初始化

package 数组;

public class array3 {
    public static void main(String[] args){
        int[] number = new int[50];

        number[0] = 1;
        number[1] = 2;
        number[2] = 3;

        System.out.println(number[0]);
        System.out.println(number[1]);
        System.out.println(number[2]);
        System.out.println(number[3]);
    }
}


//数组默认初始化值的规律
//整数类型:默认初始化值0
//小数类型:默认初始化值0.0
//字符类型:默认初始化值 \ueeee’ 空格
//布尔类型:默认初始化值 false
//引用数据类型:默认初始化值 null

---

数组练习

练习

package 数组;

import javafx.geometry.Bounds;

import javax.swing.*;
import java.util.Random;

public class arraylx2 {
    public static void main(String[] args) {
        /*需求:生成10个1~10之间的随机数存入数组
        1) 求出所有数据的和
        2)求所有数据的平均数
        3) 统计有多少个数据比平均值小*/

        //定义数组
        int[] arr = new int[10];
        //把随机数存入数组
        Random r = new Random();

        for(int i = 0;i < arr.length;i++){
            int number = r.nextInt(100) + 1;
            arr[i] = number;
        }
        //1) 求出所有数据的和
        int num = 0;
        for (int i = 0; i < arr.length; i++) {
            num = num + arr[i];
        }
        System.out.println("所有数的和是" + num);

        //2)求所有数据的平均数
        int veg = 0;
        for (int i = 0; i < arr.length; i++) {
            veg = num / arr.length;
        }
        System.out.println("所有数据的平均数为" + veg);

        //3) 统计有多少个数据比平均值小
        int conent = 0;
        for (int i = 0; i < arr.length; i++) {
            if(arr[i] < veg){
                conent = conent + 1;//conent++
            }
        }
        System.out.println("有" + conent + "个数据比平均值小");


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

---

package 数组;

public class arraylx3 {
    public static void main(String[] args) {
        /*需求: 定义一个数组，存入1,2,3,4,5。
        交换首尾索引对应的元素.交换前: 1,2,3,4,5，交换后: 5,2,3,4,1*/

        //定义数组存储数据
        int[] arr = {1, 2, 3, 4, 5};

        for (int i = 0, j = arr.length - 1; i < j; i++, j--) {
            int temp = arr[i];
            arr[i] = arr[j];
            arr[j] = temp;
        }
        for (int i = 0; i < arr.length; i++) {
            System.out.println(arr[i] + " ");
        }
    }
}