Cannot assign generic array directly to local variable

Question

Consider this code:

final public class Array<T> implements Iterable<T> {
    private T[] array;
    private int l;
    private int h;
    public Array(int L, int H) {
        @SuppressWarnings("unchecked")
        this.array =  (T[]) (new Object[H- L+1]);
        this.l = L;
        this.h = H;
    }
}

It fails to compile on my machine with the following error:

Array.java:21: error: illegal start of type
        this.array =  (T[]) (new Object[H- L+1]);
        ^
Array.java:21: error: ';' expected
        this.array =  (T[]) (new Object[H- L+1]);
            ^
2 errors

The syntax-checker/linter that is available in VSCode even complains about the following:

[Java] Syntax error, insert "enum Identifier" to complete EnumHeaderName
[Java] Syntax error, insert "EnumBody" to complete BlockStatements

after the @SupressWarnings statement.

However when I change the constructor to this:

final public class Array<T> implements Iterable<T> {
    private T[] array;
    private int l;
    private int h;
    public Array(int L, int H) {
        @SuppressWarnings("unchecked")
        final a = (T[]) (new Object[H- L+1]);
        this.array =  a;
        this.l = L;
        this.h = H;
    }
}

It works as expected.

My question is:

What can I not assign the generic array directly to my local field ? Is this a compiler bug ?

I am using the following java version on an up-to-date arch linux install.

$ java -showversion
openjdk version "1.8.0_172"
OpenJDK Runtime Environment (build 1.8.0_172-b11)
OpenJDK 64-Bit Server VM (build 25.172-b11, mixed mode)

You can't put an annotation on an assignment. See: stackoverflow.com/q/8425674 — Jorn Vernee
– Jorn Vernee, Commented Jun 24, 2018 at 16:22

NiVeR · Accepted Answer · 2018-06-24 16:26:38Z

3

The statement @SuppressWarnings("unchecked") is misplaced. Move it above the constructor like this:

@SuppressWarnings("unchecked")
public Array(int L, int H) {
    this.array =  (T[]) (new Object[H- L+1]);
    this.l = L;
    this.h = H;
}

answered Jun 24, 2018 at 16:26

NiVeR

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