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Java - immutable ArrayList in Java
4 points
In this short article, we would like to how in Java create immutable List - read-only list.
This technique can be used with all classes that implements List interface. Main advantage of this approach is: the list is only covered by class - list is not copied that makes solution very fast.
Quick solution:
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Collections.unmodifiableList(list);
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import java.util.Arrays;2
import java.util.List;3
import java.util.ArrayList;4
import java.util.Collections;5
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public class Example {7
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public static void main(String[] args) {9
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List<String> list = new ArrayList<>(Arrays.asList("one", "two", "three"));11
List<String> immutableList = Collections.unmodifiableList(list);12
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immutableList.add("four");14
}15
}Output:
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Exception in thread "main" java.lang.UnsupportedOperationException2
at java.base/java.util.Collections$UnmodifiableCollection.add(Collections.java:1060)3
at Example.main(Example.java:13)Note: in read-only list we are not able to do any modification.
