What is SuppressWarnings ("unchecked") in Java?

java generics unchecked suppress-warnings
jojo picture jojo · Jul 15, 2009 · Viewed 429.6k times · Source

Sometime when looking through code, I see many methods specify an annotation:

@SuppressWarnings("unchecked")

What does this mean?

Answer

Jon Skeet picture Jon Skeet · Jul 15, 2009

Sometimes Java generics just doesn't let you do what you want to, and you need to effectively tell the compiler that what you're doing really will be legal at execution time.

I usually find this a pain when I'm mocking a generic interface, but there are other examples too. It's usually worth trying to work out a way of avoiding the warning rather than suppressing it (the Java Generics FAQ helps here) but sometimes even if it is possible, it bends the code out of shape so much that suppressing the warning is neater. Always add an explanatory comment in that case!

The same generics FAQ has several sections on this topic, starting with "What is an "unchecked" warning?" - it's well worth a read.

Related questions

Unchecked assignment warning

I am using Android Studio 1.1.0. This causes no warning: public static class A { public Map<Integer, String> getMap() { return null; } } public static class B { public void processA(A a) { Map<Integer, String> map = a.getMap(); } } But …

Read More
How to avoid unchecked cast warnings with Java Generics

Somehow my old question was closed, so I open a new one: I am using Java Generics to implement a generic bidirectional Hash Map out of an SQL Query. It should be able to map any combination of String, Integer …

Read More
Java "unchecked call to compareTo(T) as a member of the raw type java.lang.Comparable"

I'm trying to implement a sorted list as a simple exercise in Java. To make it generic I have an add(Comparable obj) so I can use it with any class that implements the Comparable interface. But, when I use …

Read More