Static Initializations

Question 1

Give me the definition of a static initializer !

Answer 1

A static initializer is a block of code preceded by the keyword static, which is used for initializing static variables and performing any static initialization when the class is first loaded

Question 2

Give me a characteristic of the static initializer !

Answer 2

The characteristic of the static initializer is that it runs before any code in the class when the class is first loaded by the JVM.

Question 3

Give me when a static final variable should be initialized with examples and counter-examples !

Answer 3

A static final variable should be initalized inline or inside a static initializer, it can not be initialized in a constructor or in an instance initializer because that will result in a compilation error

EXAMPLE 1 :
public class Example {
static final int STATIC_FINAL_VAR = 10;
}

EXAMPLE 2 :
public class Example {
static final int STATIC_FINAL_VAR;

static {
    STATIC_FINAL_VAR = 10;
} }

**COUNTER-EXAMPLE ** :
public class Example {
static final int STATIC_FINAL_VAR;

// This would cause a compilation error
 {
     STATIC_FINAL_VAR = 10;
 }

// This would also cause a compilation error
 public Example() {
    STATIC_FINAL_VAR = 10;
 } }

Question 4

What is the difference between a static final variable and final variable with examples !

Answer 4

A static final variable can only be initialized inline or inside a static initializer while a final variable can be initialized inline, in an instance initializer, or in a constructor

Question 5

When a final instance variable should be initialized with examples and counter examples !

Answer 5

A final instance variable should be initialized inline or in an instance initializer or in a constructor and that’s it

EXAMPLE 1 :

public class Example {
final int finalInstanceVarInline = 10; // Initialized inline

final int finalInstanceVarInitializerBlock;
{
    finalInstanceVarInitializerBlock = 20; // Initialized in an instance initializer block
}

final int finalInstanceVarConstructor;

public Example(int value) {
    finalInstanceVarConstructor = value; // Initialized in a constructor
}

EXAMPLE 2 :

14 :private static int one;
15 : private static final int two;
16 : private static final int three = 3;
17 : private static final int four; /* DOES NOT COMPILE */
18 : static {
19 : one = 1;
20 : two = 2;
21 : three = 3; // DOES NOT COMPILE

• Line 14 declares a static variable that is not final. It can be assigned as many times as we like
• Line 15 declares a final variable without initializing it. This means we can initialize it exactly once in a static block.
• Line 21 doesn’t compile because this is the second attempt.
• Line 17 declares a final variable that never gets initialized