Java no name static method

What is this?

public class ABC {
   public ABC() {
         System.out.println("world");
   }
   static {
         System.out.println("hello");
   }
}

Will print: hello world

I 开发者_开发知识库don't really understand this, or what kind of method that static code is.

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It's called a "static initialisation block".

It runs when the class is first loaded; only once.

For example, a constructor will run each time the class is instantiated; the static block only runs once, when it's first loaded statically by the VM/Class loader.

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I think it's worth noting the static block will be run exactly once each time a classloader loads a class. This means if you have more than one classloader, the block can execute more than once.