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Java Java Data Structures Exploring the Java Collection Framework Sets

James Adamski
James Adamski
3,027 Points

Unsupported operation error in java-repl

Can you see the source of the error below in java-repl. I tried various solutions, including, trying to manually import the java.utils. Don't understand why it should fail here.

ava> List<String> frontEndLang = Arrays.asList("HTML","CSS","JavaScript","TypeScript");
java.util.List<java.lang.String> frontEndLang = [HTML, CSS, JavaScript, TypeScript]
java> List<String> backEndLang = Arrays.asList("Java","Python","JavaScript","PHP","Objective-C","Swift","Ruby");
java.util.List<java.lang.String> backEndLang = [Java, Python, JavaScript, PHP, Objective-C, Swift, Ruby]
java> List<String> allLangs = Arrays.asList("HTML","CSS","JavaScript","TypeScript");
java.util.List<java.lang.String> allLangs = [HTML, CSS, JavaScript, TypeScript]
java> allLangs.addAll(backEndLang);
java.lang.UnsupportedOperationException

1 Answer

Tonnie Fanadez
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Tonnie Fanadez
UX Design Techdegree Graduate 22,793 Points

James Adamski Arrays.asList() method of java.util.Arrays class acts as bridge between the standard Array and Java Collection Framework. Arrays.asList() method returns a fixed-size list meaning you cannot add or remove elements. This method is really useful when you wish to manually insert elements to a List and saves you time instead of calling .add() everytime you want to insert and element to a Collection List.

However it has a downside in that the array won't dynamic and cannot be increased/decreased in size . As an indication that the code is trying to modify a non-resizable or unmodifiable collection, UnsupportedOperationException is thrown if you try to add or remove elements.

To add/remove elements you need to wrap your list in a new ArrayList e.g.

List<String> allLangs = new ArrayList<>(Arrays.asList("HTML","CSS","JavaScript","TypeScript"));