import java.util.Arrays;

public class App {
    public static void main(String[] args) throws Exception {
        int[] arr1;
        int arr2[];
        int i, arr3[];

        i =22;
        arr3 = new int[3];

        int[] arr4 = new int[5];

        for(int x = 0; x<5; x++){
            System.out.println(arr4[x]);
        }

        arr4[0] = 22;
        System.out.println(Arrays.toString(arr4));

        //arr4[5] = 55;
        arr4[4] = 44;
        System.out.println(Arrays.toString(arr4));
        System.out.println(arr4.length);

        arr3 = new int[0];   
        System.out.println(Arrays.toString(arr3));
        System.out.println(arr3.length);

        System.out.println(arr4[0] + "" + arr4[4]);

        String str = "abc";
        char[] ch = new char[]{'a', 'b', 'c'};

        System.out.println(str.length());
        System.out.println(ch.length);

        arr1 = new int[3];
        System.out.println(arr1);
        arr1 = new int[]{4, 3, 4, 5, 3};
        System.out.println(arr1);
        
        arr1 = new int[]{1,2,3,4,5};
        // arr2 = new int[5];
        /*
        for(int x = 0; x<5; x++){
            arr2[x] = arr1[x];
        }
        */
        // arr2 = Arrays.copyOfRange(arr1, 1, 3);

        // System.arraycopy(arr1, 1, arr2, 3, 2);

        arr2 = arr1.clone();

        System.out.println(Arrays.toString(arr1));
        System.out.println(Arrays.toString(arr2));

        System.out.println(arr1);
        System.out.println(arr2);
    }
}

[edit]

3.2. 예제2 ¶

import java.util.Arrays;
import java.util.Scanner;

public class App2 {
    public static void main(String[] args) {
        int[][] arr1;
        int[] arr2[];
        int arr3[][];

        arr1 = new int[4][3];

        System.out.println(arr1);
        System.out.println(Arrays.toString(arr1));
        //System.out.println(Arrays.toString(arr1[0]));

        for(int i=0; i<arr1.length; i++){
            System.out.println(Arrays.toString(arr1[i]));
        }

        arr2 = new int[3][];

        arr2[0] = new int[3];
        arr2[1] = new int[5];
        arr2[2] = new int[4];

        for(int i=0; i<arr2.length; i++){
            System.out.println(Arrays.toString(arr2[i]));
        }

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

        Scanner sc = new Scanner(System.in);

        int x = sc.nextInt();
        arr3 = new int[x][];

        for(int i=0; i<arr3.length; i++){
            arr3[i] =  new int[sc.nextInt()];
        }

        for(int i=0; i<arr3.length; i++){
            System.out.println(Arrays.toString(arr3[i]));
        }

        sc.close();
    }
}

[edit]

3.3. 예제3 ¶

import java.util.Arrays;
import java.util.Scanner;

public class App3 {
    public static void main(String[] args) {
        Tv.model();

        Tv tv1 = new Tv();
        tv1.changeChannel(22);

        tv1.currentChannel();
   
        tv1.changeChannel("33");

        tv1.currentChannel();
        
    }
}

class Tv{
    String color;
    boolean power;
    int channel;
    static int modelNum = 2022;

    void power(){
        power = !power;
    }

    void currentChannel(){
        System.out.println("현재 채널: " + channel);
    }

    void changeChannel(int channel){
        this.channel = channel;
    }
    
    void changeChannel(String channel){
        this.channel = Integer.parseInt(channel);
    }

    static void model(){
        System.out.println("모델명: " + modelNum);
    }

    static void change(int a){
        modelNum += a;
    }

}

[edit]