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Groovy example source code file (

This example Groovy source code file ( is included in the "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 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
 * 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();

Other Groovy examples (source code examples)

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