Compile-time polymorphism in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of overloaded method calls

What is the output of the following Java program that demonstrates method overloading?

Java

public class Test {
    void display(int a) {
        System.out.println("Integer: " + a);
    }
    void display(String a) {
        System.out.println("String: " + a);
    }
    public static void main(String[] args) {
        Test obj = new Test();
        obj.display(10);
        obj.display("Hello");
    }
}

A Integer: 10\nString: Hello

B Integer: 10\nInteger: Hello

C String: 10\nString: Hello

D Compilation error due to ambiguous method calls

💡 Hint

Look at the method signatures and which one matches the argument type.

The method display is overloaded with one version accepting an int and another accepting a String. The calls match exactly one method each, so the output prints the respective labels and values.

❓ Predict Output

intermediate

Overloaded method with type promotion

What will be the output when the following Java code runs?

Java

public class Demo {
    void show(int a) {
        System.out.println("int: " + a);
    }
    void show(long a) {
        System.out.println("long: " + a);
    }
    public static void main(String[] args) {
        Demo d = new Demo();
        d.show(100);
        d.show(100L);
    }
}

A long: 100\nlong: 100

B int: 100\nlong: 100

C int: 100\nint: 100

D Compilation error due to ambiguous method call

💡 Hint

Check which method matches the argument type exactly and which uses type promotion.

The call with 100 matches the int version exactly. The call with 100L matches the long version exactly. So the output prints int: 100 and long: 100.

🔧 Debug

advanced

Identify the compile-time error in overloaded methods

Why does the following Java code cause a compile-time error?

Java

public class Sample {
    void process(int a, double b) {
        System.out.println("int and double");
    }
    void process(double a, int b) {
        System.out.println("double and int");
    }
    public static void main(String[] args) {
        Sample s = new Sample();
        s.process(5, 10);
    }
}

A No error; output is 'int and double'

B Compilation error due to duplicate method signatures

C Compilation error due to ambiguous method call s.process(5, 10)

D No error; output is 'double and int'

💡 Hint

Consider how Java chooses overloaded methods when both are applicable.

The call s.process(5, 10) is ambiguous because both methods can accept two int arguments by type promotion (int to double). The compiler cannot decide which method to call, causing a compile-time error.

📝 Syntax

advanced

Which overloaded method signature is invalid?

Which of the following overloaded method declarations in Java is invalid?

A void calculate(int a, int a) {}

B int calculate(int a, int b) {}

C void calculate(int a, int b) {}

D void calculate(double a, int b) {}

💡 Hint

Check the parameter names and whether they are unique within the method signature.

Method parameters must have unique names. Option A declares two parameters with the same name 'a', which is a syntax error.

🚀 Application

expert

Determine the output of overloaded constructors

What is the output when the following Java program runs?

Java

public class Box {
    int width, height;
    Box() {
        this(10);
        System.out.println("Default constructor");
    }
    Box(int w) {
        this(w, 20);
        System.out.println("One-arg constructor");
    }
    Box(int w, int h) {
        width = w;
        height = h;
        System.out.println("Two-arg constructor");
    }
    public static void main(String[] args) {
        Box b = new Box();
        System.out.println("Width: " + b.width + ", Height: " + b.height);
    }
}

A One-arg constructor\nTwo-arg constructor\nDefault constructor\nWidth: 10, Height: 20

B Default constructor\nOne-arg constructor\nTwo-arg constructor\nWidth: 10, Height: 20

C Compilation error due to recursive constructor calls

D Two-arg constructor\nOne-arg constructor\nDefault constructor\nWidth: 10, Height: 20

💡 Hint

Trace the constructor calls starting from the default constructor.

The default constructor calls the one-arg constructor with 10. The one-arg constructor calls the two-arg constructor with (10, 20). The two-arg constructor sets the fields and prints first. Then control returns back printing one-arg and default constructor messages. Finally, the width and height are printed.