What are the characteristics of Java static variables?

The characteristics of Java static variables are as follows:

1. Static variables belong to a class, not to an object. They are initialized when the class is loaded and are only initialized once. All objects of that class share the same static variable.
2. Static variables can be accessed anywhere without the need to create an object. They can be accessed using the class name followed by a dot operator.
3. Static variables only have one copy in memory, so they are not duplicated when multiple objects are created. If one object modifies the value of a static variable, other objects accessing that static variable will be affected.
4. Static variables can be accessed by all instance objects and by static methods. However, static methods cannot directly access non-static variables.
5. Static variables can be declared as final, meaning they are constants. Once they are assigned a value, they cannot be changed.

It is important to note that improper use of static variables can lead to thread safety issues because multiple threads share the same static variable. In a multi-threaded environment, if multiple threads simultaneously modify the value of a static variable, it may result in unexpected outcomes. Therefore, it is advisable to avoid using static variables in multi-threaded environments as much as possible.