Static blocks in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a static block in Java.

Java

class Example {
    static [1] {
        System.out.println("Static block executed");
    }
}

Drag options to blanks, or click blank then click option'

Ablock

Bfinal

Cvoid

Dstatic

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name or return type before the block.

Omitting the static keyword.

The keyword static is used to declare a static block in Java.

2fill in blank

medium

Complete the code to print a message from a static block.

Java

class Demo {
    static {
        System.out.[1]("Hello from static block");
    }
}

Drag options to blanks, or click blank then click option'

Aprintln

Bprint

Cwrite

Dprintf

Attempts:

3 left

💡 Hint

Common Mistakes

Using print which does not add a new line.

Using methods that do not exist on System.out.

The method println prints the message and moves to a new line.

3fill in blank

hard

Fix the error in the static block declaration.

Java

class Test {
    static [1]() {
        System.out.println("Static block");
    }
}

Drag options to blanks, or click blank then click option'

Astatic

Bvoid

Cblock

Dmain

Attempts:

3 left

💡 Hint

Common Mistakes

Treating static blocks like methods with parentheses.

Adding return types to static blocks.

Static blocks do not have a method name or return type. The code incorrectly uses void as a method signature, which is wrong. The correct fix is to remove the parentheses and return type entirely, but since the blank replaces the parentheses, the best fix is to remove them by replacing with an empty string. However, since the blank must be filled, the closest correction is to remove the parentheses by putting nothing, but options do not include empty string. So the correct answer is to remove the parentheses and return type, so the blank should be empty. But since options do not allow empty, the best is to put void to fix the syntax error, but this is a trick question. The correct fix is to remove the parentheses and return type entirely. So the blank should be empty, but since not possible, the best is void to fix the error.

4fill in blank

hard

Fill both blanks to create a static block that initializes a static variable.

Java

class Counter {
    static int count;
    static [1] {
        count [2] 100;
    }
}

Drag options to blanks, or click blank then click option'

Astatic

B=

C+=

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using void instead of static for the block.

Using += instead of = for assignment.

The static block is declared with static keyword and the variable count is assigned the value 100 using =.

5fill in blank

hard

Fill all three blanks to create a class with a static block that prints a message and initializes a static variable.

Java

class Init {
    static int number;
    static [1] {
        System.out.[2]("Initializing number");
        number [3] 42;
    }
}

Drag options to blanks, or click blank then click option'

Astatic

Bprintln

C=

Dprint

Attempts:

3 left

💡 Hint

Common Mistakes

Using print instead of println.

Using += instead of = for assignment.

Omitting the static keyword for the block.

The static block is declared with static. The message is printed using println, and the variable number is assigned 42 using =.

Practice

1. What is the main purpose of a static block in Java?

easy

A. To handle exceptions during runtime

B. To create instance variables for each object

C. To initialize static variables or run code once when the class loads

D. To define methods that can be overridden

Solution

1. Step 1: Understand static block behavior

   A static block runs once when the class is loaded, before any object is created.

2. Step 2: Identify its purpose

   It is mainly used to initialize static variables or run setup code that should execute once.

3. Final Answer:

   To initialize static variables or run code once when the class loads -> Option C

4. Quick Check:

   Static block purpose = initialize static variables [OK]

Hint: Static blocks run once at class load for static setup [OK]

Common Mistakes:

• Thinking static blocks run for each object
• Confusing static blocks with constructors
• Assuming static blocks handle exceptions only

2. Which of the following is the correct syntax for a static block in Java?

easy

A. static() { System.out.println("Hello"); }

B. static { System.out.println("Hello"); }

C. static void { System.out.println("Hello"); }

D. static class { System.out.println("Hello"); }

Solution

1. Step 1: Recall static block syntax

   A static block is declared with the keyword static followed by braces containing code, without parentheses or return types.

2. Step 2: Check options

   static { System.out.println("Hello"); } matches the correct syntax: static { ... }. Others incorrectly add parentheses, return types, or keywords.

3. Final Answer:

   static { System.out.println("Hello"); } -> Option B

4. Quick Check:

   Static block syntax = static { ... } [OK]

Hint: Static blocks have no parentheses or return type [OK]

Common Mistakes:

• Adding parentheses after static keyword
• Using void or other return types
• Trying to declare static block as a method

3. What will be the output of the following Java code?

class Test {
    static int x;
    static {
        x = 5;
        System.out.print("A");
    }
    static {
        x = 10;
        System.out.print("B");
    }
    public static void main(String[] args) {
        System.out.print(x);
    }
}

medium

A. AB10

B. BA10

C. AB5

D. BA5

Solution

1. Step 1: Understand static block execution order

   Static blocks run in the order they appear when the class loads. First block prints "A" and sets x=5, second prints "B" and sets x=10.

2. Step 2: Trace main method output

   Main prints the value of x after static blocks run, which is 10 (last assignment). So output is "AB10".

3. Final Answer:

   AB10 -> Option A

4. Quick Check:

   Static blocks run in order, last x=10 [OK]

Hint: Static blocks run top to bottom before main [OK]

Common Mistakes:

• Assuming static blocks run after main
• Confusing order of static blocks
• Expecting x to be 5 instead of 10

4. Identify the error in the following code snippet:

class Example {
    static {
        System.out.println("Start");
    }
    static void block() {
        System.out.println("Inside method");
    }
}

medium

A. No error, code is valid

B. Static block must have a method name

C. Static block cannot contain print statements

D. Static block cannot be followed by a static method

Solution

1. Step 1: Check static block rules

   Static blocks can contain code like print statements and do not require a method name.

2. Step 2: Verify static method declaration

   Static methods can appear after static blocks without any issue.

3. Final Answer:

   No error, code is valid -> Option A

4. Quick Check:

   Static blocks and methods can coexist [OK]

Hint: Static blocks can have code; methods are separate [OK]

Common Mistakes:

• Thinking static blocks need method names
• Assuming print statements are invalid in static blocks
• Believing static blocks and methods conflict

5. Consider this Java class:

class Config {
    static int value;
    static {
        value = 100;
        System.out.print("Init1-");
    }
    static {
        value += 50;
        System.out.print("Init2-");
    }
    static {
        if (value > 100) {
            value = 200;
            System.out.print("Init3-");
        }
    }
    public static void main(String[] args) {
        System.out.print(value);
    }
}

What is the output when this program runs?

hard

A. Init2-Init3-200

B. Init1-Init2-150

C. Init1-Init3-200

D. Init1-Init2-Init3-200

Solution

1. Step 1: Trace static blocks in order

   First block sets value=100 and prints "Init1-". Second adds 50 (value=150) and prints "Init2-". Third checks if value>100 (true), sets value=200 and prints "Init3-".

2. Step 2: Check main output

   Main prints the final value, which is 200 after all static blocks run.

3. Final Answer:

   Init1-Init2-Init3-200 -> Option D

4. Quick Check:

   Static blocks run sequentially, final value=200 [OK]

Hint: Static blocks run top to bottom, last changes persist [OK]

Common Mistakes:

• Ignoring the condition in third static block
• Assuming static blocks run in random order
• Forgetting value updates in each block