What is the Java `static {}` keyword all by itself?

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Static Block in Java

I came across the following use of static and did not figure out what it does. I am aware of using for example static String hello = "World"; but I do not understand the following.

static {
   loadFromProperties(new Properties());
}

The static block in the program is the first to execute when a VM is initialized. More specifically, the static block is used for initializing the static constants. public static final int MAX_ITER; static { int dummyMaxIter = AClass.calculateABC(); if (dummyMaxIter >= 0) { MAX_ITER = dummyMaxIter; } else { MAX_ITER = 0; } } See the above segment. can initialize the `MAX_ITER` directly from `AClass.calculateABC()`. But you need to validate the value returned by `AClass.calculateABC()` before assigning. — Mohan, Jul 17 '12 at 12:27

score 8 · Accepted Answer · edited May 23 '17 at 10:29

8

It's called a static initializer. It's a block of code that runs when the class is initialized.

Related question (probably a dup actually):

Static Block in Java

edited May 23 '17 at 10:29

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answered Jul 17 '12 at 12:12

aioobe

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is initialization different to instantiation ? – NimChimpsky Jul 17 '12 at 12:15
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@NimChimpsky: *Class* initialization happens before any instances are created (instantiation). – T.J. Crowder Jul 17 '12 at 12:15

Nandkumar Tekale · Answer 2 · 2012-07-17T12:19:00.783

3

This is called static blocks. Those are executed when class is loaded/initialized but before instantiation. You can use then to initialize static members/fields.

edited Jul 17 '12 at 12:19

answered Jul 17 '12 at 12:13

Nandkumar Tekale

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Actually it's executed when the class is *initialized*. (In practice you seldom notice the difference though.) – aioobe Jul 17 '12 at 12:14

What is the Java `static {}` keyword all by itself?

2 Answers2