Is Java KeyGenerator using Singleton Pattern?

Question

But it seems each time when the users invoke getInstance() it will create a new instance.

I should have misunderstood something.

I think it's static factory method. This link might be helpful: https://stackoverflow.com/a/3169644/8093676. — K.Miao, Sep 08 '17 at 21:50

score 2 · Accepted Answer · answered Sep 08 '17 at 21:42

The source doesn't contradict your observation:

public static final KeyGenerator getInstance(String algorithm)
        throws NoSuchAlgorithmException {
    if (algorithm == null) {
        throw new NullPointerException("algorithm == null");
    }
    Engine.SpiAndProvider sap = ENGINE.getInstance(algorithm, null);
    return new KeyGenerator((KeyGeneratorSpi) sap.spi, sap.provider, algorithm);
}

What might be a singleton is the SpiAndProvider returned by ENGINE#getInstance. If you look further into the implementation it's not surprising that there is a new instance each time you call getInstance because KeyGenerator has instance members, initiated with the parameters you pass with a call.

Is Java KeyGenerator using Singleton Pattern?

1 Answers1