javaSE数组操作随笔

数组

概念

一种常见的数据结构,能够存储一组相同类型的数据

作用

储存一组相同类型的数据结构,方便进行数理统计,也可以进行信息的展示

定义

数据类型[] 数组名;
数组名 = new 数据类型[数组的长度];
数组名 = new 数据类型[]{元素1,元素2,...,元素n}

数据类型[] 数组名 = new 数据类型 [数组的长度];

数据类型[] 数组名 = {元素1,元素2,...,元素n};

注意

栈

数据类型[] 数组名
堆

new 数据类型[5];

数组名 = new 数据类型[5];
注意不同类型默认值
注意new 数据类型[] 可以先定义再赋值

基本要素

标识符

数组名称,是专业术语,本质是变量名
数组元素

数组中每一块空间储存的元素
元素类型

数组存放的类型
元素下标

数组中每一个元素所处的位置就是数组元素的下标,从0开始,最大值为数组长度-1
特性

长度一旦定义就不能改变,除非重新赋值

数组操作

遍历

将数组中元素全部查看一遍(循环)

修改数组中的元素

ed:数列能够被三整除并放回去

public class example1 {
    public static void main(String[] args) {
        int[] numbers = {10,12,17,32,39,50};
        for (int i = 0; i < numbers.length; i++) {
            if (numbers[i] % 3 == 0) {
                int result = numbers[i]*numbers[i];
                numbers[i] *= numbers[i];
            }
        }
    }

向数组中添加元素

ABCDE F 将F插入到B后面

public class example2 {
    public static void main(String[] args) {
        String[] persionArr = {"A", "B", "C", "D", "E"};
        String[] newArr = new String[persionArr.length + 1];
        int inDex = 2;
        for (int i = 0; i < inDex; i++) {
            newArr[i] = persionArr[i];
        }
        newArr[inDex] = "F";
        for (int i = inDex ; i < persionArr.length; i++) {
            newArr[i + 1] = persionArr[i];
        }

        persionArr = newArr;
        for (int i = 0; i <persionArr.length; i++) {
            System.out.println(persionArr[i]);
        }
    }
}

删除数组中的元素

接上题,C离开

public class example3 {
    public static void main(String[] args) {
        String[] persionArr = {"A", "B", "F", "C", "D","E"};
        String[] newArr = new String[persionArr.length - 1];
        int inDex = 3;
        for (int i = 0; i < inDex; i++) {
            newArr[i] = persionArr[i];
        }
        for (int i = inDex +1; i < persionArr.length; i++) {
            newArr[i-1] = persionArr[i];
        }
        persionArr = newArr;
        for (int i = 0; i < persionArr.length; i++) {
            System.out.println(persionArr[i]);
        }
    }
}

数组拷贝与扩容

语法

System.arrayCopy(原数组,拷贝的开始位置,目标数组,存放的开始位置,拷贝的元素个数;)

示例

public class example2 {
    public static void main(String[] args) {
        String[] persionArr = {"A", "B", "C", "D", "E"};
        String[] newArr = new String[persionArr.length + 1];
        int inDex = 2;
//        for (int i = 0; i < inDex; i++) {
//            newArr[i] = persionArr[i];
//        }
//        数组拷贝
        System.arraycopy(persionArr, 0, newArr, 0, inDex);
        newArr[inDex] = "F";
//        for (int i = inDex ; i < persionArr.length; i++) {
//            newArr[i + 1] = persionArr[i];
//        }
        System.arraycopy(persionArr, inDex, newArr, inDex +1, persionArr.length - inDex);
        persionArr = newArr;
        for (int i = 0; i <persionArr.length; i++) {
            System.out.println(persionArr[i]);
        }
    }
}

public class example3 {
    public static void main(String[] args) {
        String[] persionArr = {"A", "B", "F", "C", "D","E"};
        String[] newArr = new String[persionArr.length - 1];
        int inDex = 3;
//        for (int i = 0; i < inDex; i++) {
//            newArr[i] = persionArr[i];
//        }
        System.arraycopy(persionArr, 0, newArr, 0, inDex);
//        for (int i = inDex +1; i < persionArr.length; i++) {
//            newArr[i-1] = persionArr[i];
//        }
        System.arraycopy(persionArr, inDex + 1, newArr, inDex, newArr.length - inDex -1);
        persionArr = newArr;
        for (int i = 0; i < persionArr.length; i++) {
            System.out.println(persionArr[i]);
        }
    }
}

数组扩容

见第四行第七行

public class example4 {
    public static void main(String[] args) {
        String[] persionArr = {"A", "B", "C", "D","E"};
        String[] newArr = Arrays.copyOf(persionArr, persionArr.length+1);
        int inDex = 2;
        //A B C D E null =>A B C C D E
        System.arraycopy(newArr, inDex, newArr, inDex+1, persionArr.length - inDex);
        //A B C C D E =>A B F C D E
        newArr[inDex] = "F";
        persionArr = newArr;
        for (int i = 0; i < persionArr.length; i++){
            System.out.println(persionArr[i]);

        }
    }
}

二维数组

数组排序

数组中的元素从小到大或从大到小顺序依次排列

冒泡排序

基本定义跟冒泡一样

ed:

public class example5 {
    public static void main(String[] args) {
        int [] number = {10,70,55,80,25,60};
        for(int i=0;i<number.length;i++){
            for(int j=0;j<number.length -i - 1;j++){
                if (number[j] < number[j+1]) {
                    int temp = number[j];
                    number[j] = number[j+1];
                    number[j+1] = temp;
                }
            }
        }
        for(int i=0;i<number.length;i++){
            System.out.println(number[i]);
        }
    }
}

工具类的排序操作

语法

Array.sort(数组名);//将数组中的元素进行升序排列
Arrays.toString(数组名);//将数组中的元素组装为一个字符串

import java.util.Arrays;

public class example5 {
    public static void main(String[] args) {
        int [] number = {10,70,55,80,25,60};
        for(int i=0;i<number.length;i++){
            for(int j=0;j<number.length -i - 1;j++){
                if (number[j] < number[j+1]) {
                    int temp = number[j];
                    number[j] = number[j+1];
                    number[j+1] = temp;
                }
            }
        }
//        for(int i=0;i<number.length;i++){
//            System.out.println(number[i]);
            System.out.println(Arrays.toString(number));
        
    }
}

import java.util.Arrays;

public class example6 {
    public static void main(String[] args) {
        char [] chars = {'c','a','g','p','f'};
        Arrays.sort(chars);//对数组进行深序排序
        System.out.println(Arrays.toString(chars));
        String [] names = {"zhangsan","zhangsi","liso","lisib","lisan"};
        Arrays.sort(names);
        System.out.println(Arrays.toString(names));
    }
}

二分查找法

又称折半查找以中间分为两个区间,利用中间元素与目标元素比较大小,从而确定目标元素所处的区间,依次往复执行,直到找到目标元素为止

二分查找只适用于已经排好序的数组

ed:从95,93,87,86,79,72,60,53中快速找出元素60所处位置

public class example7 {
    public static void main(String[] args) {
        int [] numbers = {95,93,87,86,79,72,60,53};
        int target = 60;
        int start = 0;
        int end = numbers.length - 1;
        while (start < end) {
            int mid = (start + end) / 2;
            if (numbers[mid] > 60) {
                start = mid + 1;
            }else if (numbers[mid] < 60) {
                end = mid -1;
            }else {
                System.out.println("目标元素"+target +"所处位置:" + mid);
                break;
            }
        }
    }
}

二维数组

public class example8 {
   public static void main(String[] args) {
       String[][] personInfos = new String[10][3];

       double[][] agesAndScores = new double[5][2];
       agesAndScores[0] = new double[]{18,60};
       agesAndScores[1] = new double[]{19,65};
       agesAndScores[2] = new double[]{28,90};
       agesAndScores[3] = new double[]{22,55};
       agesAndScores[4] = new double[]{21,60};

       String[][] infos = new String[5][];
       infos[0] = new String[]{"刘德华"};
       infos[1] = new String[]{"张学友","很牛逼"};
       infos[2] = new String[]{"张三","学渣","整天不务正业","吃喝嫖赌样会"};

   }
}

public class example9 {
    public static void main(String[] args) {
        String[][] musicInfos = new String[5][3];
        Scanner sc = new Scanner(System.in);
        for (int i = 0; i < musicInfos.length; i++) {
            System.out.println("Enter music name: ");
            String name = sc.next();
            System.out.println("Enter singer name: ");
            String singer = sc.next();
            System.out.println("Enter music public time: ");
            String date = sc.next();
            musicInfos[i] = new String[] {name, singer, date};
        }
    }
}

public class example10 {
    public static void main(String[] args) {
        double[][][] stuInfos = new double[3][][];
        stuInfos[0] = new double[10][2];
        stuInfos[1] = new double[8][2];
        stuInfos[2] = new double[7][2];
        Scanner sc = new Scanner(System.in);
        for (int i = 0; i < stuInfos.length; i++) {
            for (int j = 0; j < stuInfos[i].length; j++) {
                System.out.print("Enter student ages: ");
                int age = sc.nextInt();
                System.out.println("Enter student achievement: ");
                double achievement = sc.nextDouble();
                stuInfos[i][j] = new double[]{age,achievement};
            }
        }
        for (int i = 0; i < stuInfos.length; i++) {
            double totalAge = 0,totalAchievement = 0;
            for (int j = 0; j < stuInfos[i].length; j++) {
                totalAge += stuInfos[i][j][0];
                totalAchievement += stuInfos[i][j][1];
            }
            System.out.println("average ages: " + totalAge/stuInfos.length
            + "\naverage achievement: " + totalAchievement/stuInfos.length);
        }
    }
}

posted @ 2025-12-17 19:39 程玖浔阅读(3) 评论(0) 收藏举报

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chengjiuxun

javaSE数组操作随笔

数组

概念

作用

定义

注意

基本要素

数组操作

二维数组

二维数组

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