The objects in the List were references, right? Confirmation of

Memorandum on processing the contents of the List

Tested because I felt that the objects in the List were not references

Prepare a test class

public class Test {
	public static void main(String[] args) {
		TestEntity enttity = new TestEntity();
		TestEntity enttity2 = new TestEntity();
		TestEntity enttity3 = new TestEntity();

		ArrayList<TestEntity> list = new ArrayList<>();
		list.add(enttity);
		list.add(enttity2);
		list.add(enttity3);

		showEntityList(list);
	}

	static void showEntityList(ArrayList<TestEntity> list) {
		System.out.println("Look at the contents of the entity");

		for (TestEntity a : list) {
			System.out.println(a.a);
			System.out.println(a.b);
			System.out.println(a.c);
			System.out.println(a.d);
		}
	}
}

public class TestEntity {
	String a = "start";
	String b = "b";
	String c = "c";
	String d = "d";

}

Execution result

Look at the contents of the entity
start
b
c
d
start
b
c
d
start
b
c
d

When you touch the contents of the extracted object

Prepare method

	/**
	 *Just take out the entity and process it
	 * */
	static void modifyOnly(ArrayList<TestEntity> list) {
		int size = list.size();

		for (int i=0;i<size; i++) {
			TestEntity value = list.get(i);
			value.a = "Hajima Rides(" + i + ")";
			value.b = "2(" + i + ")";
			value.c = "3(" + i + ")";
			value.d = "4(" + i + ")";
		}
	}

Try using the above

		TestEntity enttity = new TestEntity();
		TestEntity enttity2 = new TestEntity();
		TestEntity enttity3 = new TestEntity();

		ArrayList<TestEntity> list = new ArrayList<>();
		list.add(enttity);
		list.add(enttity2);
		list.add(enttity3);

		modifyOnly(list);
		showEntityList(list);

Execution result

Look at the contents of the entity
Hajima Rides(0)
2(0)
3(0)
4(0)
Hajima Rides(1)
2(1)
3(1)
4(1)
Hajima Rides(2)
2(2)
3(2)
4(2)

Conclusion

Just taking it out and processing the contents will affect the contents of the List.

It's strange, if I did this at work, it wouldn't be rewritten, and if I set the rewritten entity again, it did what I wanted. Well, this movement is exactly what I expected.

Well, it's a staring contest with the source of the workplace.

Postscript

Thanks to @shiracamus, I learned how to make the source on Qiita easier to read. Thank you for not knowing how to use Qiita before technical matters.

You can point out and merge. However, it is a secret (sweat) that when I checked the contents of the indication after fixing it by hand without knowing it, it was in a merged state and on the contrary the correction became strange.