java数组

Posted 2022-12-09 程序员大宝(coder-dabao)

package com.clevercode.javastudy.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;

public class ArrayStudy 

    public static void main(String[] args) 
        ArrayStudy a1 = new ArrayStudy();
        a1.collectionToArray();
    

    //声明数组，然后在分配内存
    public boolean testInt() 
        //声明数组
        int a[];
        //分配内存
        a = new int[10];


        for (int i = 0; i < 10; i++) 
            a[i] = i + 100;
        

        for (int i = 0; i < 10; i++) 
            System.out.println(a[i]);
        

        for (int item : a) 
            System.out.println(item);
        

        return true;
    

    //声明数组，同时初始化
    public String testInt2() 
        //方式1
        int arr[] = new int[]1, 2, 3, 4, 5;
        //方式2
        int arr2[] = 6, 7, 8, 9, 10;

        for (int i = 0; i < arr.length; i++) 
            System.out.println("arr,i=" + i + ",value=" + arr[i]);
        

        for (int i = 0; i < arr2.length; i++) 
            System.out.println("arr2,i=" + i + ",value=" + arr2[i]);
        

        return "OK";
    

    //声明二维数组，然后分配内存
    public String testInt3() 
        int arr[][];
        arr = new int[2][4];

        int arr2[][];
        arr2 = new int[2][];
        arr2[0] = new int[3];
        arr2[1] = new int[4];

        return "OK";
    

    //声明二维数组，同时初始化
    public String testInt4() 
        int arr[][] = 1, 2, 3, 4;
        int arr2[][] = new int[3][4];
        for (int i = 0; i < arr.length; i++) 
            for (int j = 0; j < arr[i].length; j++) 
                System.out.println(arr[i][j]);
            
        
        return "OK";
    

    //声明数组，然后在分配内存
    public boolean testString() 
        String arr[] = "fbc", "efg", "zfg";

        for (int i = 0; i < arr.length; i++) 
            System.out.println(arr[i]);
        

        for (String item : arr) 
            System.out.println(item);
        
        return true;
    

    //对数组进行排序
    public boolean stringSort() 
        String arr[] = "fbc", "efg", "zfg";
        Arrays.sort(arr);
        for (String item : arr) 
            System.out.println(item);
        
        return true;
    

    //数组转成集合
    public boolean arrayToCollection()
    
        String arr[] = "caojun","hello world","haodf";

        //Arrays.asList返回的固定长度列表，不能add和remove
        List<String> list = Arrays.asList(arr);
        //list.add("new");
        //list.remove("clevercode");

        List<String> list2 = new ArrayList<>(Arrays.asList(arr));
        list2.add("new");
        list2.remove("clevercode");
        System.out.println(list2);
        return true;
    

    //集合转成数组
    public boolean collectionToArray()
    
        List<String> list = new ArrayList<String>();
        list.add("A");
        list.add("B");
        list.add("C");

        // 使用泛型，无需显式类型转换
        String[] array = list.toArray(new String[list.size()]);
        System.out.println(array[0]);

        HashSet<Integer> set = new HashSet<>();
        set.add(3);
        set.add(4);
        set.add(1);
        Object arr[] = set.toArray();
        System.out.println(arr[0]);
        return true;
    

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