_DelayedConversionToString.java

/*
 * Copyright 2014 Attila Szegedi, Daniel Dekany, Jonathan Revusky
 * 
 * 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,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package freemarker.core;

/** Don't use this; used internally by FreeMarker, might changes without notice. */
public abstract class _DelayedConversionToString {

    private static final String NOT_SET = new String();

    private Object object;
    private volatile String stringValue = NOT_SET;

    public _DelayedConversionToString(Object object) {
        this.object = object;
    }

    @Override
    public String toString() {
        String stringValue = this.stringValue;
        if (stringValue == NOT_SET) {
            synchronized (this) {
                stringValue = this.stringValue;
                if (stringValue == NOT_SET) {
                    stringValue = doConversion(object);
                    this.stringValue = stringValue; 
                    this.object = null;
                }
            }
        }
        return stringValue;
    }

    protected abstract String doConversion(Object obj);

}