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import java.util.ArrayList; public class ArrayListRetainAllExample2 { ArrayList<String> numbers = null; System.out.println(numbers); // null ArrayList<String> retainedNumbers = new ArrayList<>(); retainedNumbers.add("1"); retainedNumbers.add("2"); System.out.println(retainedNumbers); // [1, 2] retainedNumbers.retainAll(numbers); // throw NullPointerException }
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