Static vs non-static behavior in Java - Practice Questions

trophy

Challenge - 5 Problems

💻 code output

intermediate

Output of static and instance variable access

What is the output of this Java program?

Java

public class Test {
    static int staticVar = 5;
    int instanceVar = 10;

    public static void main(String[] args) {
        Test obj1 = new Test();
        Test obj2 = new Test();
        obj1.staticVar = 20;
        obj2.instanceVar = 30;
        System.out.println(obj1.staticVar + "," + obj1.instanceVar);
        System.out.println(obj2.staticVar + "," + obj2.instanceVar);
    }
}

A

5,30
20,10

B

20,10
20,30

C

20,30
20,10

D

5,10
5,30

🧠 conceptual

intermediate

Static method access to instance variables

Which statement about static methods in Java is true?

A Static methods cannot access any variables.

B Static methods can access instance variables only if they are final.

C Static methods can only access static variables directly.

D Static methods can directly access instance variables without an object.

🔧 debug

advanced

Identify the error in static and non-static context

What error will this code produce?

Java

public class Demo {
    int x = 10;
    static void printX() {
        System.out.println(x);
    }
    public static void main(String[] args) {
        printX();
    }
}

A Compile-time error: non-static variable x cannot be referenced from a static context

B Runtime NullPointerException

C Prints 10

D Compile-time error: missing return statement

💻 code output

advanced

Output of static block and instance block execution order

What is the output when this Java program runs?

Java

public class Blocks {
    static {
        System.out.println("Static block");
    }
    {
        System.out.println("Instance block");
    }
    public Blocks() {
        System.out.println("Constructor");
    }
    public static void main(String[] args) {
        new Blocks();
        new Blocks();
    }
}

A

Static block
Instance block
Constructor
Instance block
Constructor

B

Instance block
Constructor
Instance block
Constructor
Static block

C

Static block
Constructor
Instance block
Constructor
Instance block

D

Constructor
Instance block
Static block
Constructor
Instance block

🚀 application

expert

Predict the value of static and instance counters

Consider this Java class that counts instances and total calls. What will be the output after main runs?

Java

public class Counter {
    static int totalCalls = 0;
    int instanceCalls = 0;

    public Counter() {
        totalCalls++;
        instanceCalls++;
    }

    public void call() {
        totalCalls++;
        instanceCalls++;
    }

    public static void main(String[] args) {
        Counter c1 = new Counter();
        Counter c2 = new Counter();
        c1.call();
        c2.call();
        System.out.println("c1: " + c1.instanceCalls + ", c2: " + c2.instanceCalls + ", total: " + totalCalls);
    }
}

A c1: 2, c2: 2, total: 6

B c1: 1, c2: 1, total: 4

C c1: 3, c2: 3, total: 8

D c1: 2, c2: 2, total: 4