What is static imports and what is its importance in java

Question

While reading some java books, I came to know about static imports. I have some doubts in my mind.

1. What is static imports.
2. When and why to use it.

Explaination with examples will be helpful.

Answer 1

One example is JUnit tests

import static org.junit.Assert.assertEquals;
 ...
 assertEquals(x, y);

Answer 2

Imports are typing shortcuts. A "regular" import is a shortcut down to the class level...

import java.util.List 

Let's you just use

List l;

Instead of

java.util.List l;

A static import is a shortcut down to the method level. The method must be static, since there is no instance to associate with it...

import static java.lang.Math.abs

Lets you just use

x = abs(y);

instead of

x = java.lang.Math.abs(y);

Imports do not effect your compiled output or running code in any way. Once something is compiled there's no way to tell if the original source had imports or not.