Java example source code file (Basic.java)

This example Java source code file (Basic.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

basic, hashset, printstream, serviceloader, set, string, system, testloader, thread, util

The Basic.java Java example source code

/*
 * Copyright (c) 2005, 2012, 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.
 */

//

import java.io.*;
import java.util.*;


public class Basic {

    private static PrintStream out = System.err;

    private static <T> Set setOf(Iterable it) {
        Set<T> s = new HashSet();
        for (T t : it)
            s.add(t);
        return s;
    }

    private static <T> void checkEquals(Set s1, Set s2, boolean eq) {
        if (s1.equals(s2) != eq)
            throw new RuntimeException(String.format("%b %s : %s",
                                                     eq, s1, s2));
    }

    static abstract class TestLoader {
        String name;

        TestLoader(String name) { this.name = name; }

        abstract ServiceLoader<FooService> load();
    }

    static TestLoader tcclLoader = new TestLoader("Thread context class loader") {
        ServiceLoader<FooService> load() {
            return ServiceLoader.load(FooService.class);
        }
    };

    static TestLoader systemClLoader = new TestLoader("System class loader") {
        ServiceLoader<FooService> load() {
            return ServiceLoader.load(FooService.class, ClassLoader.getSystemClassLoader());
        }
    };

    static TestLoader nullClLoader = new TestLoader("null (defer to system class loader)") {
        ServiceLoader<FooService> load() {
            return ServiceLoader.load(FooService.class, null);
        }
    };

    public static void main(String[] args) {
        for (TestLoader tl : Arrays.asList(tcclLoader, systemClLoader, nullClLoader)) {
            test(tl);
        }
    }

    static void test(TestLoader tl) {
        ServiceLoader<FooService> sl = tl.load();
        out.format("%s: %s%n", tl.name, sl);

        // Providers are cached
        Set<FooService> ps = setOf(sl);
        checkEquals(ps, setOf(sl), true);

        // The cache can be flushed and reloaded
        sl.reload();
        checkEquals(ps, setOf(sl), false);

    }
}