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Groovy example source code file (LazyReference.java)

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

Java - Groovy tags/keywords

init, init, lazyreference, lockableobject, managedreference, managedreference, null_reference, null_reference, referencebundle, string, t, t

The Groovy LazyReference.java source code

 * Copyright 2003-2010 the original author or authors.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *     http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.
package org.codehaus.groovy.util;

 * Soft reference with lazy initialization under lock
public abstract class LazyReference<T> extends LockableObject {
    private static final ManagedReference INIT = new ManagedReference(ReferenceType.HARD,null,null){};
    private static final ManagedReference NULL_REFERENCE = new ManagedReference(ReferenceType.HARD,null,null){};
    private ManagedReference<T> reference = INIT;
    private final ReferenceBundle bundle;
    public LazyReference(ReferenceBundle bundle) { 
        this.bundle = bundle;
    public T get() {
        ManagedReference<T> resRef = reference;
        if (resRef == INIT) return getLocked(false);
        if (resRef == NULL_REFERENCE) return null;
        T res = resRef.get();
        // res== null means it got collected
        if (res==null) return getLocked(true);
        return res;

    private T getLocked (boolean force) {
        lock ();
        try {
            ManagedReference<T> resRef = reference;
            if (!force && resRef != INIT) return resRef.get();
            T res = initValue();
            if (res == null) {
                reference = NULL_REFERENCE;
            } else {
                reference = new ManagedReference<T>(bundle,res);
            return res;
        } finally {

    public void clear() {
        reference = INIT;

    public abstract T initValue();

    public String toString() {
        T res = reference.get();
        if (res == null)
          return "<null>";
          return res.toString();

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