Java基础--数组

数组概述

数组是相同类型数据的有序集合。

数组 描述的是相同类型的若干数据，按照一定的先后次序排列组合而成。

数组中的每一个数据称为一个元素，通过下标访问数组。

数组创建

package array;

public class Demo01 {
    public static void main(String[] args) {
        int[] numbers;  //1.声明一个数组
        numbers = new int[10];  //2.分配空间
        //3. 赋值
        numbers[0] = 1;
        numbers[1] = 2;
        numbers[2] = 3;
        numbers[3] = 4;
        numbers[4] = 5;
        numbers[5] = 6;
        numbers[6] = 7;
        numbers[7] = 8;
        numbers[8] = 9;
        numbers[9] = 10;
        System.out.println(numbers[2]);
        int sum = 0;
        for (int i = 0; i <numbers.length ; i++) {
            sum += numbers[i];
        }
        System.out.println("总和为：" + sum);
    }
}

package array;

public class Demo02 {
    public static void main(String[] args) {
        // 静态初始化
        int[] a = {1,2,3,4,5};
        Man[] man = {new Man(),new Man()};
        //动态初始化
        int[] b = new int[10];
        b[0] = 10;
        System.out.println(b[0]);
        System.out.println(b[1]);
        
    }
}

数组使用

package array;

import java.sql.PreparedStatement;

public class Demo03 {
    public static void main(String[] args) {
        int[] array = {1,2,3,4,5};
        //遍历
        for (int i = 0; i < array.length ; i++) {
            System.out.println(array[i]);
        }
        //求和
        int sum = 0;
        for (int i = 0; i < array.length ; i++) {
            sum += array[i];
        }
        System.out.println(sum);
        //找最大数
        int max = array[0];
        for (int i = 0; i <array.length ; i++) {
            if(array[i] > max){
                max = array[i];
            }
        }
        System.out.println(max);

        //for each
        for (int arr:array
             ) {
            System.out.println(arr);
        }

        //反转数组
        int[] result = new int[array.length];
        for (int i = 0, j = array.length-1; i < array.length; i++,j--) {
            result[i] = array[j];
        }
        for (int res:result
             ) {
            System.out.println(res);
        }
    }
}

多维数组

package array;
public class Demo04 {
    public static void main(String[] args) {
        int[][] arrays = {{1,2,3},{4,5,6}};
        for (int i = 0; i < 2 ; i++) {
            for (int j = 0; j <arrays[0].length ; j++) {
                System.out.println(arrays[i][j]);
            }
        }
    }
}

Arrays类

package array;

import java.util.Arrays;

public class ArraysDemo {
    public static void main(String[] args) {
        int[] a = {1,2,5,3,343,56,43,45454};
        System.out.println(Arrays.toString(a));
        Arrays.sort(a); //排序，升序
        System.out.println(Arrays.toString(a));
        Arrays.fill(a,0);  //填充
        //Arrays.fill(a,2,3,4);
        System.out.println(Arrays.toString(a));
    }

    public static void PrintArray(int[] a){

        for (int i = 0; i <a.length ; i++) {
            if (i == 0) {
                System.out.print("[");
            }
            if (i == a.length - 1) {
                System.out.print(a[i] + "]");
            } else {
                System.out.print(a[i] + ", ");
            }
        }
    }

}

冒泡排序

package array;

import java.util.Arrays;

public class BubbleSort {
    public static void main(String[] args) {
        int[] a = {1,3,2,4,9,6,5,7,8};
        System.out.println(Arrays.toString(a));
        int[] sort = bubleSort(a);
        System.out.println(Arrays.toString(sort));
    }
    public static int[] bubleSort(int[] a){
        for (int i = 0; i <a.length-1 ; i++) {
            boolean flag = false;
            for (int j = 0; j <a.length-1-i; j++) {
                if(a[j]>a[j+1]){
                    int t = a[j];
                    a[j] = a[j+1];
                    a[j+1] = t;
                    flag = true;
                }
            }
            if(flag==false){
                break;
            }
        }
        return a;
    }
}

稀疏数组

package array;

import java.util.Arrays;

//稀疏数组
public class xisushuzu {
    public static void main(String[] args) {
        int[][] a = new int[11][11];
        a[1][2] = 1;
        a[2][3] =2;
        System.out.println("原始数组：");
        for (int[] arr:a) {
            for (int ar:arr) {
                System.out.print(ar+"\t");
            }
            System.out.println();
        }
        int count=0;
        for (int i = 0; i < a.length ; i++) {
            for (int j = 0; j <a[i].length; j++) {
                if(a[i][j]!=0){
                    count++;
                }
            }
        }
        int[][] xisu = new int[count+1][3];
        xisu[0][0] = a.length;
        xisu[0][1] = a[0].length;
        xisu[0][2] = count;
        int k = 1;
        for (int i = 0; i < a.length ; i++) {
            for (int j = 0; j <a[i].length; j++) {
                if(a[i][j]!=0){
                    xisu[k][0] = i;
                    xisu[k][1] = j;
                    xisu[k][2] = a[i][j];
                    k++;
                }
            }
        }
        System.out.println("稀疏数组：");
        for (int i = 0; i <= count ; i++) {
            System.out.println(Arrays.toString(xisu[i]));
        }
        //稀疏数组还原
        //1. 读取稀疏数组的值
        int[][] arrr = new int[xisu[0][0]][xisu[0][1]];
        for (int i = 1; i <xisu.length ; i++) {
            arrr[xisu[i][0]][xisu[i][1]] = xisu[i][2];
        }
        System.out.println("还原数组:");
        for (int[] br:arrr) {
            for (int b:br) {
                System.out.print(b+"\t");
            }
            System.out.println();
        }

    }
}