JuniorTheoryCommon

What happens when this program is compiled and run?

JAVA

import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> xs = List.of("a");
        xs.add("b");
        System.out.println(xs);
    }
}

An UnsupportedOperationException is thrown

Expecting [a, b]: List.of creates an immutable list, and add, remove and set on it throw; copy it into new ArrayList<>(...) to change it.
Expecting a compile error: the type List declares add, so the call compiles; the list refuses the change only at run time.

How do you get a list you can change from List.of("a")?
What happens if you call set(0, "b") on the same list?

Back to questions Open topic in roadmap →Answer it yourself — Quiz

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JuniorTheoryCommon

What happens when this program is compiled and run?

JAVA

import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> xs = List.of("a");
        xs.add("b");
        System.out.println(xs);
    }
}

An UnsupportedOperationException is thrown

Expecting [a, b]: List.of creates an immutable list, and add, remove and set on it throw; copy it into new ArrayList<>(...) to change it.
Expecting a compile error: the type List declares add, so the call compiles; the list refuses the change only at run time.

How do you get a list you can change from List.of("a")?
What happens if you call set(0, "b") on the same list?

Back to questions Open topic in roadmap →Answer it yourself — Quiz