Java数组的简单概括

Java数组

• 定义：相同类型数据的有序集合

• 声明：

int[] nums;

• 创建：

nums = new int[10];

• 声明加创建：（动态初始化（包含默认初始化））

int[] nums= new int[10];

• 获取数组长度：

int a = nums.length;

• 静态初始化：

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

• 数组的基本特点
  • 长度确定
  • 元素类型一致
  • 元素类型不限
  • 数组变量为引用类型，数组可看成对象，数组中的每个元素相当于该对象的成员变量
  • 数组本身就是对象，Java保存在堆中
• 数组边界：[0,length-1]

数组的使用

• For-Each循环

  int[] a={1,2,3,4,5,6,7};
          for (int i : a) {
              System.out.println(i);
          }
  

• 数组做方法入参

  public static void main(String[] args) {
          int[] a={1,2,3,4,5,6,7};
          printArray(a);
      }
      public static void printArray(int[] arrays){
          for (int i = 0; i < arrays.length; i++) {
              System.out.println(arrays[i]);
          }
      }
  

• 数组做返回值(反转数组)

  public static void main(String[] args) {
          int[] arrays={1,2,3,4,5,6,7};
          printArray(reverse(arrays));
      }
      //数组做方法入参
      public static void printArray(int[] arrays){
          for (int i = 0; i < arrays.length; i++) {
              System.out.println(arrays[i]);
          }
      }
      //数组反转
      public static int[] reverse(int[] arrays){
          int[] result = new int[arrays.length];
          for (int i = 0,j=arrays.length-1; i < arrays.length; i++,j--) {
              result[j]=arrays[i];
          }
          return result;
      }
  

多维数组

• 定义

  int[][] arrays = {{1,2},{2,3},{3,4},{4,5}};//二维数组
  

• 遍历二维数组

  int[][] arrays = {{1,2},{2,3},{3,4},{4,5}};
      for (int i = 0; i < arrays.length; i++) 
      {
          for (int j = 0; j < arrays[i].length; j++){
              System.out.println(arrays[i][j]);
          }      
      }
  

Arrays类

• 打印数组元素:Arrays.toString()
• 自动排序(升序)：Arrays.sort()
• 等

冒泡排序

import java.lang.reflect.Array;
import java.util.Arrays;
public class Demo {
    public static void main(String[] args) {
        int[] array = {7,4,3,56,5,2,9};
        int[] sort = sort(array);
        System.out.println(Arrays.toString(sort));
    }
    public static int[] sort(int[] array){
        int temp = 0;
        for (int i = 0; i < array.length-1; i++) {
            for (int j = 0; j < array.length-1-i; j++) {
                if (array[j]<array[j+1]){
                    temp = array[j];
                    array[j] = array[j+1];
                    array[j+1] = temp;
                }
            }
        }
        return array;
    }
}

稀疏数组

public class Demo99 {
    public static void main(String[] args) {
        //创建一个棋盘 11*11 0：没有棋子 ，1：黑棋 ，2：白棋
        int[][] array = new int[11][11];
        array[1][2]=1;
        array[2][3]=2;
        System.out.println("输出原始的数组");
        for (int[] ints : array) {
            for (int anInt : ints) {
                System.out.print(anInt+"\t");
            }
            System.out.println(" ");
        }
        System.out.println("====================================");
        //生成稀疏数组
        //遍历有效值，得出稀疏数组的行数
        int sum = 0;
        for (int[] ints : array) {
            for (int anInt : ints) {
                if (anInt!=0){
                    sum++;
                }
            }
        }
        System.out.println("有效值为："+sum);
        //创建稀疏数组
        int[][] array2 = new int[sum+1][3];
        array2[0][0]=array.length;
        array2[0][1]=array.length;
        array2[0][2]=sum;
        int count = 0;
        for (int i = 0; i < array.length; i++) {
            for (int j = 0; j < array.length; j++) {
                if (array[i][j]!=0){
                    count++;
                    array2[count][0]=i;
                    array2[count][1]=j;
                    array2[count][2]=array[i][j];
                }
            }
        }
        //遍历输出稀疏数组
        for (int[] ints : array2) {
            for (int anInt : ints) {
                System.out.print(anInt+"\t");
            }
            System.out.println(" ");
        }
        System.out.println("=====================================");
        //还原数组
        int[][] array3 = new int[array2[0][0]][array2[0][1]];
        for (int i = 1; i < array2.length; i++) {
            array3[array2[i][0]][array2[i][1]]=array2[i][2];
        }
        for (int[] ints : array3) {
            for (int anInt : ints) {
                System.out.print(anInt+"\t");
            }
            System.out.println(" ");
        }
    }
}
----------------------------输出------------------------------------
    输出原始的数组
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	 
====================================
有效值为：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