Java Immutable Blog

DeepCopy.java

List<Integer> list1 = new ArrayList<>();
list1.add(1);
List<Integer> list2 = new ArrayList<>(list1);
list1.add(2);

NonStrictlyImmutable.java

public class NonStrictlyImmutable {
	private final List<Integer> mList = new ArrayList<>();
	
	public List<Integer> getList() {
		return mList;
	}
}

ShallowCopy.java

List<Integer> list1 = new ArrayList<>();
list1.add(1);
List<Integer> list2 = list1;
list1.add(2);

StrictlyImmutable.java

public class StrictlyImmutable {
	private final List<Integer> mList = new ArrayList<>();
	
	public List<Integer> getList() {
		// 以下两种方式都可以，各有优劣
		// return new ArrayList<>(mList);
		// return Collections.unmodifiableList(mList);
		
		return Collections.unmodifiableList(mList);
	}
}