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Asked: 2026-05-23T18:56:02+00:00

I just wonder what usage the following code has: public class Sub extends java.util.ArrayList<String>

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I just wonder what usage the following code has:

public class Sub extends java.util.ArrayList<String> {...}

There is no any compiling restriction on the generic constraint java.util.ArrayList<String>.

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  1. Editorial Team

    Let’s say you were making an index for a book, but you don’t know how many indices you will need. You could make a class BookIndex extends ArrayList<String> or if you want to get really picky: BookIndex extends ArrayList<IndexEntry>.

    /e1
    Also, when a one Class extends a generic Class like ArrayList<String> you can grab the String out from the generic declaration, unlike if you had a class ArrayList<T>. In ArrayList<T> you would never be able to figure out what the T is.

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