Menu
A Static Initialization Block in Java is a block that runs before the main( ) method in Java. Java does not care if this block is written after the main( ) method or before the main( ) method, it will be executed before the main method( ) regardless.
Instance variables are initialized using initialization blocks. However, the static initialization blocks can only initialize the static instance variables. These blocks are only executed once when the class is loaded.
Initialization of Instance variables But if you declare an instance variable static and final Java compiler will not initialize it in the default constructor therefore, it is mandatory to initialize static and final variables. If you don't a compile time error is generated.
Initializer block contains the code that is always executed whenever an instance is created. It is used to declare/initialise the common part of various constructors of a class. The order of initialization constructors and initializer block doesn't matter, initializer block is always executed before constructor.
A static initialization blocks allows more complex initialization, for example using conditionals:
static double a;
static {
if (SomeCondition) {
a = 0;
} else {
a = 1;
}
}
Or when more than just construction is required: when using a builder to create your instance, exception handling or work other than creating static fields is necessary.
A static initialization block also runs after the inline static initializers, so the following is valid:
static double a;
static double b = 1;
static {
a = b * 4; // Evaluates to 4
}
A typical usage:
private final static Set<String> SET = new HashSet<String>();
static {
SET.add("value1");
SET.add("value2");
SET.add("value3");
}
How would you do it without static initializer?
You can use try/catch block inside static{} like below:
MyCode{
static Scanner input = new Scanner(System.in);
static boolean flag = true;
static int B = input.nextInt();
static int H = input.nextInt();
static{
try{
if(B <= 0 || H <= 0){
flag = false;
throw new Exception("Breadth and height must be positive");
}
}catch(Exception e){
System.out.println(e);
}
}
}
PS: Referred from this!
Exception handling during initialization is another reason. For example:
static URL url;
static {
try {
url = new URL("https://blahblah.com");
}
catch (MalformedURLException mue) {
//log exception or handle otherwise
}
}
This is useful for constructors that annoyingly throw checked exceptions, like above, or else more complex initialization logic that might be exception-prone.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With