can’t java unchecked exceptions be handled using try/catch block?

The only difference between checked and unchecked exceptions is that checked ones have to be either caught or declared in the method signature using throws, whereas with unchecked ones this is optional.

Unchecked Exception can’t be handled by your code i.e. we can’t use try/catch block

Sure we can – but we don’t have to.

Also i think throw keyword can be used only with try/catch block.can throw Keyword be used with Unchecked Exception?

Note that there are two keywords:

• throw explicitly throws an exception object you created. throw new NullPointerException(); works perfectly fine, though explicitly creating that particular exception is uncommon and most would consider it bad style.
• throws declares that a method may throw that exception. With unchecked exceptions this is optional, but can be useful to document the fact (again, one would normally not declared throws NullPointerException because that is pretty much a given).