Java: ArrayList initialization assignment

test environment

$ java -version
java version "1.8.0_251"
Java(TM) SE Runtime Environment (build 1.8.0_251-b08)
Java HotSpot(TM) 64-Bit Server VM (build 25.251-b08, mixed mode)

method one:

conventional way

List<Integer> list = new ArrayList<>();
list.add(1);
list.add(5);
System.out.println(list);
// [1, 5]

Method 2:

addAll method

List<Integer> obj = new ArrayList<>();

List<Integer> list = Arrays.asList(1, 2, 3);

obj.addAll(list);

System.out.println(obj);
// [1, 2, 3]

Method 3:

Arrays.asList() method

List<Integer> list = new ArrayList<>(Arrays.asList(1, 2, 3));

System.out.println(list);
// [1, 2, 3]

Method 4:

anonymous inner class

List<String> list = new ArrayList<String>() {
    
    
    {
    
    
        add("1");
        add("2");
    }
};

System.out.println(list);
// [1, 2]

full code

package com.example;

import org.junit.jupiter.api.Test;

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

public class ArrayTest {
    
    
    @Test
    public void testInit1() {
    
    
        List<Integer> list = new ArrayList<>();
        list.add(1);
        list.add(5);
        System.out.println(list);
        // [1, 5]
    }

    @Test
    public void testInit2() {
    
    
        List<Integer> obj = new ArrayList<>();

        List<Integer> list = Arrays.asList(1, 2, 3);

        obj.addAll(list);

        System.out.println(obj);
        // [1, 2, 3]
    }

    @Test
    public void testInit3() {
    
    
        List<Integer> list = new ArrayList<>(Arrays.asList(1, 2, 3));

        System.out.println(list);
        // [1, 2, 3]
    }

    @Test
    public void testInit4() {
    
    
        List<String> list = new ArrayList<String>() {
    
    
            {
    
    
                add("1");
                add("2");
            }
        };

        System.out.println(list);
        // [1, 2]
    }
}

Refer to
the initialization of ArrayList in Java