1、数组概述

1）数组的定义

  • 相同类型数据的有序集合
  • 数组元素：每一个数据
  • 访问：每个数组元素可通过下表来访问

    2、数组声明创建

    1）代码示例

    ```java package com.array;

public class Demo01 { public static void main(String[] args) { // 1、 声明数组 // 2、创建数组 // 3、赋值 int [] nums; nums = new int[10]; } }

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  2. ### 3、数组使用
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  4. #### 1) 内存分析
  5. ![image.png](https://cdn.nlark.com/yuque/0/2021/png/12881754/1622365996943-0813680f-4e33-4ace-9290-2e8a3ab71fe3.png#clientId=u665660f6-df33-4&from=paste&height=276&id=udca58e6f&margin=%5Bobject%20Object%5D&name=image.png&originHeight=552&originWidth=1475&originalType=binary&size=346491&status=done&style=none&taskId=ud3c28486-97ec-45eb-abb2-cfa42b5d33b&width=737.5)<br />![image.png](https://cdn.nlark.com/yuque/0/2021/png/12881754/1622366354052-b858ce4b-8357-4a7d-99cc-5eeaf3c199d1.png#clientId=u665660f6-df33-4&from=paste&height=311&id=u009aee4a&margin=%5Bobject%20Object%5D&name=image.png&originHeight=622&originWidth=1117&originalType=binary&size=84862&status=done&style=none&taskId=u8d85b89c-ebf1-4137-85c1-c61e7662573&width=558.5)
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  7. #### 2) 三种初始化
  8. ```java
  9. package com.array;
  11. public class Demo02 {
  12.     public static void main(String[] args) {
  13.         // 1、静态初始化: 创建 + 赋值
  14.         int [] a = {1,2,3,4,5,6,7,8,9};
  16.         // 2、动态初始化 包含默认初始化值是0
  17.         int [] b = new int[2];
  18.         b[0] = 1;
  19.         System.out.println(b[0]); // 1
  20.         System.out.println(b[1]); // 0
  22.         //数组的默认初始化
  23.         /*
  24.             数组是引用类型，元素相当于类的实例变量，因此数组一经分配空间，其中的每个元素也被按照实例变量同样的方式被隐式初始化
  25.          */
  27.     }
  28. }

3) 数组的四个特点

image.png

4) 数组边界

image.png

5）数组使用

  • for-each循环
  • 数组作方法入参
  • 数组作返回值 ```java package com.array;

import java.util.Arrays;

public class Demo03 { public static void main(String[] args) { int[] nums = {1,2,3,4,5};

// for (int array:nums) { // System.out.println(array); // } // printArrays(nums); int [] reverArrays = reverseArrays(nums); for (int item: reverArrays) { System.out.println(item); } } // 数组作为方法入参 public static void printArrays(int[] arrays){ for(int i = 0; i < arrays.length; i ++){ System.out.println(arrays[i]); } } // 数组作为返回值 反转数组 public static int [] reverseArrays(int [] arrays){ int [] result = new int [arrays.length]; for(int i = 0,j = arrays.length -1; i < arrays.length; i ++,j —){ result [i] = arrays[j]; } return result; }

}

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  2. ### 4、多维数组
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  4. #### 1) 代码示例
  5. ```java
  6.         int [] [] arraysTwo = {{1,2},{3,4}};
  7.         for (int [] itemArray:
  8.              arraysTwo) {
  9.             for (int item:
  10.                  itemArray) {
  11.                 System.out.println(item);
  12.             }
  13.         }

5、Arrays 类

1) 定义

image.png

2) 冒泡排序

image.png

  1. package com.array;
  3. import java.util.Arrays;
  5. public class Demo04 {
  6.     public static void main(String[] args) {
  7.         int [] arrays = {1,2,3,4,5};
  8.         System.out.println(Arrays.toString(arrays));
  9.     }
  10. }
  12. #####################################
  13. package com.array;
  15. import java.util.Arrays;
  17. public class Demo04 {
  18.     public static void main(String[] args) {
  19.         int [] arrays = {1,2,3,4,5};
  20.         int [] srotArrays = sortArrays(arrays);
  21.         for (int item:
  22.              srotArrays) {
  23.             System.out.println(item);
  24.         }
  25.     }
  26.     public static int [] sortArrays(int [] arrays){
  27.         for(int i = 0;i < arrays.length-1; i ++){
  28.             int temp = 0;
  29.             boolean flag = false;
  30.             for (int j = 0; j< arrays.length -1-i; j ++){
  31.                 if (arrays[j+1] > arrays[j]){
  32.                     temp = arrays[j];
  33.                     arrays[j] = arrays[j+1];
  34.                     arrays[j+1] = temp;
  35.                     flag = true;
  36.                 }
  37.             }
  38.             if(!flag){
  39.                 break;
  40.             }
  41.         }
  42.         return arrays;
  43.     }
  44. }

6、稀疏数组

  • 概念 - 记录有效值，变成新数组

    1) 问题引用

    image.png

    2) 定义

    image.png ```java package com.array;

public class Demo05 { public static void main(String[] args) { // 1、创建一个二维数组，11*11， 0：没有棋子 1-黑棋 2-白棋 int [] [] originArrays = new int[11][11]; originArrays[1][2] = 1; originArrays[2][3] = 2; // 2、输出原始数组 for (int[] originArray : originArrays) { for (int item : originArray) { System.out.print(item + “\t”); } System.out.println(); } // 3、转换稀疏数组保存 // 获取有效值个数 int sum = 0; for(int i = 0; i < originArrays.length; i ++ ){ for (int j = 0; j < originArrays.length; j++) { if(originArrays[i][j] != 0){ sum ++; } } } System.out.println(“有效值个数：” + sum); // 创建稀疏数组的数组 int [][] array02 = new int[sum+1][3]; array02[0][0] = 11; array02[0][1] = 11; array02[0][2] = sum;

  1.     int count = 0;
  2.     // 读取稀疏数组
  3.     for (int i = 0; i < originArrays.length; i++) {
  4.         for (int j = 0; j < originArrays.length; j++) {
  5.             if(originArrays[i][j] != 0){
  6.                 count ++ ;
  7.                 array02[count][0] = i;
  8.                 array02[count][1] = j;
  9.                 array02[count][2] = originArrays[i][j];
  10.             }
  11.         }
  12.     }
  13.     System.out.println("##############################");
  14.     for (int [] array:
  15.          array02) {
  16.         for (int item:
  17.              array) {
  18.             System.out.print(item + "\t");
  19.         }
  20.         System.out.println();
  21.     }
  22.     System.out.println("###############################");
  23.     // 还原
  24.     int [][] array03 = new int[array02[0][0]][array02[0][1]];
  25.     for (int i = 1; i < array02.length; i++) {
  26.         array03[array02[i][0]][array02[i][1]] = array02[i][2];
  27.     }
  28.     for (int [] array:
  29.          array03) {
  30.         for (int item:
  31.              array) {
  32.             System.out.print(item + "\t");
  33.         }
  34.         System.out.println();
  35.     }
  36. }

}

#

F:\my-learning\ES\jdk1.8.0_251\bin\java.exe “-javaagent:F:\java\IntelliJ IDEA 2021.1\lib\idea_rt.jar=53029:F:\java\IntelliJ IDEA 2021.1\bin” -Dfile.encoding=UTF-8 -classpath F:\my-learning\ES\jdk1.8.0_251\jre\lib\charsets.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\deploy.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\access-bridge-64.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\cldrdata.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\dnsns.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\jaccess.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\jfxrt.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\localedata.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\nashorn.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\sunec.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\sunjce_provider.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\sunmscapi.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\sunpkcs11.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\ext\zipfs.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\javaws.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\jce.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\jfr.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\jfxswt.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\jsse.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\management-agent.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\plugin.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\resources.jar;F:\my-learning\ES\jdk1.8.0_251\jre\lib\rt.jar;F:\javacode\JavaSE\out\production\基础语法;F:\javacode\JavaSE\lib\kotlin-stdlib.jar;F:\javacode\JavaSE\lib\kotlin-reflect.jar;F:\javacode\JavaSE\lib\kotlin-test.jar;F:\javacode\JavaSE\lib\kotlin-stdlib-jdk7.jar;F:\javacode\JavaSE\lib\kotlin-stdlib-jdk8.jar com.array.Demo05 0 0 0 0 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 0 0 0
0 0 0 2 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
有效值个数：2

#

11 11 2
1 2 1
2 3 2

#

0 0 0 0 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 0 0 0
0 0 0 2 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0

进程已结束，退出代码为 0 ```