Java Holiday Calendar 2016 (Day 6): Be Lazy With Java 8

Today's tip is about lazy initialization. Sometimes, we want our classes to do only what is absolutely necessary and nothing more. Immutable classes are particularly good candidates for laziness. Speedment, a Stream ORM Java toolkit and runtime, is using Lazy internally — and you can find the complete Lazy source code here. It's free, so steal it!

By Copying This Small Lazy Class...

public final class Lazy<T> {
    private volatile T value;
    public T getOrCompute(Supplier<T> supplier) {
        final T result = value;  // Read volatile just once...
        return result == null ? maybeCompute(supplier) : result;
    }
    private synchronized T maybeCompute(Supplier<T> supplier) {
        if (value == null) {
            value = requireNonNull(supplier.get());
        }
        return value;
    }
}

...You Can Do This

public class Point {
    private final int x, y;
    private final Lazy<String> lazyToString;
    public Point(int x, int y) {
        this.x = x; 
        this.y = y;
        lazyToString = new Lazy<>();
    }
    @Override
    public String toString() {
        return lazyToString.getOrCompute( () -> "(" + x + ", " + y + ")");
    }
    // The calculation of the toString value is only done once
    // regardless if toString() is called one or several times.
    //
    // If toString() is never called, then the toString value is never
    // calculated.
}

And there you have it! Your code is nice and lazy. Follow the Java Holiday Calendar 2016 with small tips and tricks all the way through the winter holiday season.