Java example source code file (BridgeMethod.java)

This example Java source code file (BridgeMethod.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

assertionerror, bridgemethod\:\:bar, class, hashset, object, reflection, set, string, util

The BridgeMethod.java Java example source code

/*
 * Copyright (c) 2011, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/**
 * @test
 * @bug 8003280
 * @summary Add lambda tests
 *   Test bridge methods in certain SAM conversion
 * @compile BridgeMethod.java
 * @run main BridgeMethod
 */

import java.lang.reflect.Method;
import java.util.HashSet;
import java.util.Set;

public class BridgeMethod {

    interface H {Object m();}

    interface K<T> {void m(T t);}

    interface L extends K<String> {} //generic substitution

    interface M {void m(String s);}

    interface KM extends K<String>, M{} //generic substitution

    interface N extends H {String m();} //covariant return

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

    static void bar(String s) {
        System.out.println("BridgeMethod.bar(String) " + s);
    }

    String moo() {
        return "moo";
    }

    private static Set<String> setOfStringObject() {
        Set<String> s = new HashSet<>();
        s.add("java.lang.String");
        s.add("java.lang.Object");
        return s;
    }

    public static void main(String[] args) {
        L la = BridgeMethod::bar; //static reference
        la.m("hi");
        Class<? extends L> c1 = la.getClass();
        Method[] methods = c1.getDeclaredMethods();
        Set<String> types = setOfStringObject();
        System.out.println("methods in SAM conversion of L:");
        for(Method m : methods) {
            System.out.println(m.toGenericString());
            assertTrue(m.getName().equals("m"));
            Class[] parameterTypes = m.getParameterTypes();
            assertTrue(parameterTypes.length == 1);
            assertTrue(types.remove(parameterTypes[0].getName()));
        }
        assertTrue(types.isEmpty() || (types.size() == 1 && types.contains("java.lang.String")));

        KM km = BridgeMethod::bar;
        //km.m("hi"); //will be uncommented when CR7028808 fixed
        Class<? extends KM> c2 = km.getClass();
        methods = c2.getDeclaredMethods();
        types = setOfStringObject();
        System.out.println("methods in SAM conversion of KM:");
        for(Method m : methods) {
            System.out.println(m.toGenericString());
            assertTrue(m.getName().equals("m"));
            Class<?>[] parameterTypes = m.getParameterTypes();
            assertTrue(parameterTypes.length == 1);
            assertTrue(types.remove(parameterTypes[0].getName()));
        }
        assertTrue(types.isEmpty());

        N n = new BridgeMethod()::moo; //instance reference
        assertTrue( n.m().equals("moo") );
        assertTrue( ((H)n).m().equals("moo") );
        Class<? extends N> c3 = n.getClass();
        methods = c3.getDeclaredMethods();
        types = setOfStringObject();
        System.out.println("methods in SAM conversion of N:");
        for(Method m : methods) {
            System.out.println(m.toGenericString());
            if (m.getName().equals("m")) {
                Class<?> returnType = m.getReturnType();
                assertTrue(types.remove(returnType.getName()));
            }
        }
        assertTrue(types.size() == 1); //there's a bridge
    }
}