Java数组

声明

dataType[] arrayRefVar;		//首选的方法
dataType arrayRefVar[];		//效果相同

使用new操作符创建数组

dataTpye[] arrayRefVar = new dataType[arraySize]

获取数组长度

arrays.length

静态初始化

int[] a = {1,2,3,4,5};

动态初始化

int[] b = new int[10];
b[0] = 10;

默认初始化

int数组默认值为0，string数组默认类型为null

For-Each循环

int[] arrays = {1,2,3,4,5};
for(int array : arrays){
    System.out.println(array);
}

数组作方法入参

public static void printArray(int[] arrays){
    for(int i = 0; i < arrays.length; i++){
        System.out.prit(arrays[i] + "");
    }
}

public static void main(String[] args){
    printArray(arrays);
}

数组作为返回值

public static int[] reverse(int[] arrays){
    int[] result = new int[arrays.length];
    
    for(int i = 0, j = result.length-1; i < arrays.length; i++,j--){
        result[j] = arrays[i];
    }
    
    return result;
}

public static void main(String[] args){
    int[] reverse = reverse(arrays);
    printArray(reverse);
}

二维数组

int a[][] = new int[2][5];
int[][] array = {{1,2},{2,3},{3,4},{4,5}};
printArray(array[0])	//1 2
System.out.println(array[0][0])		//1
System.out.println(array[0][1])		//2

int[] a = {1,3,2,4,6,5}；
Arrays.sort(a);		//数组进行排序：升序
System.out.println(Arrays.toString(a));	//打印整个数组
Arrays.fill(a,2,4,0);	//将数组2-4位填充为0

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+1] > array[j]){
                temp = array[j];
                array[j] = array[j+1];
                array[j+1] = temp;
            }
        }
    }
    return array;
}

public static void main(String[] args){
    int[] a = {1,4,2,3,5,6};
    int[] result = sort(a);
    
    System.out.println(Arrays.toString(result));
}

package com.bit.array;

public class SparseArray {
    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[][] array1 = new int[11][11];
        array1[1][2] = 1;
        array1[2][3] = 2;
        array1[3][4] = 1;
        //输出原始数组
        System.out.println("输出原始的数组");

        for(int[] ints : array1){
            for(int anInt : ints){
                System.out.print(anInt + "t");
            }
            System.out.println();
        }

        System.out.println("===================================");

        //转换为稀疏数组保存
        //获取有效值个数
        int sum = 0;
        for (int i = 0; i < 11; i++){
            for (int j = 0; j < 11; j++) {
                if(array1[i][j] != 0){
                    sum++;
                }
            }
        }

        //2.创建稀疏数组
        int[][] array2 = new int[sum+1][3];

        array2[0][0] = 11;
        array2[0][1] = 11;
        array2[0][2] = sum;

        //遍历二维数组，将非零值存在稀疏数组中
        int count = 0;
        for (int i = 0; i < array1.length; i++) {
            for (int j = 0; j < array1[i].length; j++) {
                if(array1[i][j] != 0){
                    count++;
                    array2[count][0] = i;
                    array2[count][1] = j;
                    array2[count][2] = array1[i][j];
                }
            }
        }

        //输出稀疏数组
        System.out.println("稀疏数组");
        System.out.println("行数 列数 有效值(个数)");

        for (int i = 0; i < array2.length; i++) {
            System.out.println(array2[i][0] + "t" + array2[i][1] + "t" + array2[i][2] + "t");
        }

        System.out.println("===================================");
        System.out.println("还原");

        //1.读取稀疏数组
        int[][] array3 = new int[array2[0][0]][array2[0][1]];

        //2.给其中的元素还原他的值
        for (int i = 1; i < array2.length; i++) {
            array3[array2[i][0]][array2[i][1]] = array2[i][2];
        }

        //3.打印
        System.out.println("输出原始数组");

        for(int[] ints : array3){
            for(int anInt : ints){
                System.out.print(anInt + "t");
            }
            System.out.println();
        }


    }
}