langtools/test/tools/javac/lambda/LambdaConv08.java

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/*
 * @test
 * @bug 8003280
 * @summary Add lambda tests
 *  check that SAM conversion handles covarinat return types correctly
 * @author  Peter Levart
 * @author  Maurizio Cimadamore
 * @run main LambdaConv08
 */

public class LambdaConv08 {

    static int assertionCount = 0;

    static void assertTrue(boolean cond) {
        assertionCount++;
        if (!cond)
            throw new AssertionError();
    }

    public interface ObjectF { Object invoke(); }
    public interface StringF extends ObjectF { String invoke(); }

    public static void call(StringF stringFunc) {
        assertTrue(true);
    }

    public static void call(ObjectF objectFunc) {  }

    public static void main(String[] args)   {
        call(()-> "Hello");
        assertTrue(assertionCount == 1);
    }
}