org.glassfish.grizzly.utils.Holder Maven / Gradle / Ivy

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package org.glassfish.grizzly.utils;

/**
 * The object holder, which might be used for lazy object initialization.
 * 
 * @author Alexey Stashok
 */
public abstract class Holder {
    public static  Holder staticHolder(final T value) {
        return new Holder() {

            @Override
            public T get() {
                return value;
            }
        };
    }
    
    public static IntHolder staticIntHolder(final int value) {
        return new IntHolder() {

            @Override
            public int getInt() {
                return value;
            }
        };
    }

    public static  LazyHolder lazyHolder(final NullaryFunction factory) {
        return new LazyHolder() {

            @Override
            protected T evaluate() {
                return factory.evaluate();
            }
        };
    }
    
    public static LazyIntHolder lazyIntHolder(final NullaryFunction factory) {
        return new LazyIntHolder() {

            @Override
            protected int evaluate() {
                return factory.evaluate();
            }
        };
    }
    
    public abstract E get();
    
    @Override
    public String toString() {
        final E obj = get();
        return obj != null ? "{" + obj + "}" : null;
    }

    
    public static abstract class LazyHolder extends Holder {
        private volatile boolean isSet;
        private E value;
        
        @Override
        public final E get() {
            if (isSet) {
                return value;
            }
            
            synchronized (this) {
                if (!isSet) {
                    value = evaluate();
                    isSet = true;
                }
            }
            
            return value;
        }
        
        protected abstract E evaluate();
    }    
    
    public static abstract class IntHolder extends Holder {
        @Override
        public final Integer get() {
            return getInt();
        }

        public abstract int getInt();
    }
    
    public static abstract class LazyIntHolder extends IntHolder {
        private volatile boolean isSet;
        private int value;
        
        @Override
        public final int getInt() {
            if (isSet) {
                return value;
            }
            
            synchronized (this) {
                if (!isSet) {
                    value = evaluate();
                    isSet = true;
                }
            }
            
            return value;
        }
        
        protected abstract int evaluate();
    }
}