Why static is needed in Java - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a static variable in Java.

Java

public class Example {
    public [1] int count = 0;
}

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

Astatic

Bfinal

Cprivate

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'final' instead of 'static' which makes the variable constant, not shared.

Using 'void' which is only for methods, not variables.

The keyword static makes the variable belong to the class, not instances.

2fill in blank

medium

Complete the code to call a static method from the class without creating an object.

Java

public class Calculator {
    public static int add(int a, int b) {
        return a + b;
    }

    public static void main(String[] args) {
        int sum = Calculator.[1](5, 3);
        System.out.println(sum);
    }
}

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

Asum

Badd

Ccalculate

Dtotal

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call the method without the class name or without creating an object.

Using a method name that does not exist.

The static method add is called using the class name without creating an object.

3fill in blank

hard

Fix the error in accessing a non-static variable from a static method by completing the code.

Java

public class Counter {
    static int count = 0;

    public static void increment() {
        [1]++;
    }
}

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

Acount

Bthis.count

CCounter.count

Dstatic count

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'this' inside a static method causes an error.

Trying to access instance variables directly from static methods.

To access a non-static variable from a static method, you must use an object or make the variable static. Here, using Counter.count assumes count is static.

4fill in blank

hard

Fill both blanks to create a static method that returns the square of a number.

Java

public class MathUtil {
    public [1] int square(int num) {
        return num [2] num;
    }
}

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

Astatic

B*

C+

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '*' which adds instead of multiplies.

Not declaring the method as static.

The method is declared static so it belongs to the class. The multiplication operator * calculates the square.

5fill in blank

hard

Fill all three blanks to create a static block that initializes a static variable.

Java

public class Config {
    public static String setting;

    static [1] {
        setting = [2];
    }

    public static void main(String[] args) {
        System.out.println([3]);
    }
}

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

Ablock

B"default"

Csetting

Dstatic

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to name the static block 'block' which is not a keyword.

Using the variable name incorrectly in the print statement.

The static block runs once to initialize the static variable setting with the value "default". Then it is printed in main.

Practice

1. Why do we use the static keyword in Java?

easy

A. To allow inheritance from other classes

B. To make a member belong to the class rather than any object

C. To make a method private

D. To create a new object automatically

Solution

1. Step 1: Understand what static means

   The static keyword means the member belongs to the class itself, not to any individual object.

2. Step 2: Compare with other options

   Creating objects, privacy, and inheritance are unrelated to static.

3. Final Answer:

   To make a member belong to the class rather than any object -> Option B

4. Quick Check:

   Static means class-level member = D [OK]

Hint: Static means shared by class, not by objects [OK]

Common Mistakes:

• Thinking static creates objects
• Confusing static with private access
• Assuming static controls inheritance

2. Which of the following is the correct way to declare a static method in Java?

easy

A. public static void myMethod() {}

B. static void public myMethod() {}

C. public void static myMethod() {}

D. void static public myMethod() {}

Solution

1. Step 1: Recall Java method declaration order

   In Java, the correct order is access modifier, then static, then return type, then method name.

2. Step 2: Check each option

   public static void myMethod() {} follows this order: public static void myMethod(). Others have incorrect order.

3. Final Answer:

   public static void myMethod() {} -> Option A

4. Quick Check:

   Access modifier + static + return type = A [OK]

Hint: Remember: access modifier before static before return type [OK]

Common Mistakes:

• Placing static after method name
• Omitting static keyword
• Wrong order of keywords

3. What will be the output of this code?

class Test {
    static int count = 0;
    Test() {
        count++;
    }
    public static void main(String[] args) {
        new Test();
        new Test();
        System.out.println(count);
    }
}

medium

A. Compilation error

B. 1

C. 0

D. 2

Solution

1. Step 1: Understand static variable behavior

   The static variable count is shared by all objects of the class. Each time a new object is created, the constructor increments count.

2. Step 2: Count object creations

   Two objects are created with new Test() twice, so count becomes 2.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   Static count increments twice = 2 [OK]

Hint: Static variables keep shared count across all objects [OK]

Common Mistakes:

• Thinking count resets for each object
• Confusing static with instance variables
• Expecting compilation error due to static

4. Identify the error in this code:

class Demo {
    static void show() {
        System.out.println("Hello");
    }
    public static void main(String[] args) {
        show();
        Demo d = new Demo();
        d.show();
    }
}

medium

A. Cannot call static method using object reference

B. Missing return type in show method

C. No error, code runs fine

D. Static method cannot access System.out

Solution

1. Step 1: Check static method calls

   Static methods can be called using class name or object reference. Both show() and d.show() are valid.

2. Step 2: Verify method declaration and usage

   The method show() has correct return type void and uses System.out.println correctly.

3. Final Answer:

   No error, code runs fine -> Option C

4. Quick Check:

   Static methods callable via object or class = B [OK]

Hint: Static methods can be called via object or class name [OK]

Common Mistakes:

• Thinking static methods can't be called on objects
• Assuming missing return type error
• Believing static can't use System.out

5. You want to count how many times a method is called across all objects of a class. Which approach is best?

hard

A. Use a static variable incremented inside the method

B. Use an instance variable incremented inside the method

C. Create a new object each time and count in constructor

D. Use a local variable inside the method to count calls

Solution

1. Step 1: Understand counting across all objects

   To count calls across all objects, the counter must be shared by all instances, so it must be static.

2. Step 2: Evaluate other options

   Instance variables count per object, local variables reset each call, and creating new objects won't track method calls properly.

3. Final Answer:

   Use a static variable incremented inside the method -> Option A

4. Quick Check:

   Shared counter needs static variable = C [OK]

Hint: Use static variable to share count across all objects [OK]

Common Mistakes:

• Using instance variable which counts per object only
• Using local variable which resets every call
• Counting in constructor unrelated to method calls