Java platform and JVM overview - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of JVM Bytecode Execution

What is the output of the following Java program when run on the JVM?

Java

public class Main {
    public static void main(String[] args) {
        int x = 5;
        int y = 10;
        int z = x + y;
        System.out.println(z);
    }
}

A 5 + 10

B 15

C Compilation error

D 510

💡 Hint

Remember that the + operator adds numbers in Java.

The program adds two integers 5 and 10, resulting in 15, which is printed.

🧠 Conceptual

intermediate

Role of JVM in Java Platform

Which of the following best describes the role of the JVM in the Java platform?

A It interprets compiled Java bytecode and manages memory and execution on any platform.

B It compiles Java source code directly into machine code specific to the operating system.

C It converts Java bytecode into Python code for cross-language compatibility.

D It only checks syntax errors in Java source code before compilation.

💡 Hint

Think about how Java achieves platform independence.

The JVM runs Java bytecode on any platform by interpreting it and managing execution and memory.

🔧 Debug

advanced

Identify the JVM Error

What error will the JVM throw when running this code?

Java

public class Main {
    public static void main(String[] args) {
        int[] arr = new int[3];
        System.out.println(arr[5]);
    }
}

A ArrayIndexOutOfBoundsException

B ClassCastException

C NullPointerException

D No error, prints 0

💡 Hint

Check the array index used for access.

Accessing index 5 in an array of size 3 causes ArrayIndexOutOfBoundsException at runtime.

📝 Syntax

advanced

Identify JVM Bytecode Syntax Error

Which option contains a syntax error that prevents JVM from running the code?

Java

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello JVM");
    }
}

A

ublic class Main {
    public static void main(String[] args) {
        System.out.println("Hello JVM");
    }
}

B

}
}    
;)"MVJ olleH"(nltnirp.tuo.metsyS        
{ )sgra ][gnirtS(niam diov citats cilbup    
{ niaM ssalc cilbup

C

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello JVM");
    }
}

D

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello JVM");
    }

💡 Hint

Look carefully at punctuation in the code.

Option C is missing a semicolon after the print statement, causing a syntax error.

🚀 Application

expert

JVM Memory Management Behavior

Given this Java code snippet, what will be the state of the heap after execution?

Java

public class Main {
    public static void main(String[] args) {
        String a = new String("test");
        String b = a;
        a = null;
        System.gc();
    }
}

A The string object "test" is deleted from heap before System.gc() is called.

B The string object "test" is eligible for garbage collection immediately after a = null.

C The string object "test" is moved to stack memory after System.gc().

D The string object "test" remains in heap because b still references it.

💡 Hint

Consider which variables still reference the object.

Since b still references the string object, it is not eligible for garbage collection.