Compile-time polymorphism in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a method named add that takes two integers and returns their sum.

Java

public int add(int a, int b) {
    return a [1] b;
}

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

The add method should return the sum of a and b. The plus sign + adds two numbers.

2fill in blank

medium

Complete the code to overload the add method to accept two double values.

Java

public double add(double a, double b) {
    return a [1] b;
}

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

A-

B*

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using operators other than addition.

The overloaded add method should add two double values using the + operator.

3fill in blank

hard

Fix the error in the method signature to correctly overload the add method with three integer parameters.

Java

public int add(int a, int b, [1] c) {
    return a + b + c;
}

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

Aint

Bdouble

CString

Dfloat

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different data type like double or String for the third parameter.

The method overload requires three integer parameters, so the third parameter must be int.

4fill in blank

hard

Fill both blanks to create two overloaded multiply methods: one for two integers and one for two doubles.

Java

public int multiply(int a, int b) {
    return a [1] b;
}

public double multiply(double a, double b) {
    return a [2] b;
}

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition or division instead of multiplication.

Both methods multiply their parameters using the * operator.

5fill in blank

hard

Fill all three blanks to create overloaded concatenate methods: one for two strings, one for three strings, and one for an array of strings.

Java

public String concatenate(String a, String b) {
    return a [1] b;
}

public String concatenate(String a, String b, String c) {
    return a [2] b [3] c;
}

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

A+

B-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using arithmetic operators other than plus for strings.

String concatenation in Java uses the + operator to join strings.

Practice

1.

What is compile-time polymorphism in Java?

easy

A. Using different method names for different tasks

B. Changing the method behavior at runtime based on object type

C. Using the same method name with different parameters in the same class

D. Creating multiple classes with the same name

Solution

1. Step 1: Understand method overloading

   Compile-time polymorphism is also called method overloading, where methods share the same name but differ in parameters.

2. Step 2: Differentiate from runtime polymorphism

   Runtime polymorphism uses method overriding, changing behavior based on object type at runtime, not compile-time.

3. Final Answer:

   Using the same method name with different parameters in the same class -> Option C

4. Quick Check:

   Compile-time polymorphism = method overloading [OK]

Hint: Same method name, different parameters means compile-time polymorphism [OK]

Common Mistakes:

• Confusing compile-time with runtime polymorphism
• Thinking method overriding is compile-time polymorphism
• Believing different method names are polymorphism

2.

Which of the following is the correct syntax for method overloading in Java?

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

easy

A. return a + b + c;

B. return a + b;

C. return a * b * c;

D. return a - b - c;

Solution

1. Step 1: Check method parameters

   The second add method has three parameters, so it should add all three values.

2. Step 2: Write correct return statement

   Return the sum of a, b, and c to correctly overload the add method.

3. Final Answer:

   return a + b + c; -> Option A

4. Quick Check:

   Overloaded method sums all parameters [OK]

Hint: Overloaded methods must handle all their parameters correctly [OK]

Common Mistakes:

• Returning sum of only two parameters in three-parameter method
• Using wrong operators like multiplication or subtraction
• Syntax errors like missing semicolon

3.

What will be the output of the following Java code?

class Demo {
    void show(int a) { System.out.println("Int: " + a); }
    void show(String a) { System.out.println("String: " + a); }
}
public class Test {
    public static void main(String[] args) {
        Demo d = new Demo();
        d.show(5);
        d.show("Hello");
    }
}

medium

A. Int: 5\nString: Hello

B. String: 5\nInt: Hello

C. Int: 5\nInt: Hello

D. Compilation error

Solution

1. Step 1: Identify overloaded methods

   There are two show methods: one takes int, the other takes String.

2. Step 2: Match method calls to parameters

   d.show(5) calls show(int), printing "Int: 5"; d.show("Hello") calls show(String), printing "String: Hello".

3. Final Answer:

   Int: 5\nString: Hello -> Option A

4. Quick Check:

   Method overloading calls correct method by parameter type [OK]

Hint: Method chosen by parameter type at compile time [OK]

Common Mistakes:

• Confusing parameter types and outputs
• Expecting runtime polymorphism behavior
• Thinking it causes compilation error

4.

Find the error in this code snippet related to compile-time polymorphism:

class Test {
    void display(int a) { System.out.println(a); }
    void display(int a, int b) { System.out.println(a + b); }
    void display(int a) { System.out.println(a * 2); }
}

medium

A. Incorrect method parameter types

B. Duplicate method display(int a) causes compilation error

C. Missing return type in one method

D. No error, code compiles fine

Solution

1. Step 1: Check method signatures

   Two methods have the exact same name and parameter list: display(int a).

2. Step 2: Understand method overloading rules

   Method overloading requires different parameter lists; duplicate signatures cause compilation error.

3. Final Answer:

   Duplicate method display(int a) causes compilation error -> Option B

4. Quick Check:

   Duplicate method signatures cause compile error [OK]

Hint: Overloaded methods must differ in parameter list [OK]

Common Mistakes:

• Thinking method bodies affect overloading
• Ignoring duplicate parameter lists
• Assuming code compiles without error

5.

Consider this class:

class Printer {
    void print(int a) { System.out.println("Number: " + a); }
    void print(String a) { System.out.println("Text: " + a); }
    void print(int a, String b) { System.out.println(a + " and " + b); }
}

Which call will cause a compile-time error?

hard

A. print("Test")

B. print(10, "Hello")

C. print(5)

D. print("Hello", 10)

Solution

1. Step 1: Check method signatures

   Methods accept (int), (String), and (int, String) parameters.

2. Step 2: Match call parameters

   print("Hello", 10) tries to call (String, int), which does not exist, causing compile error.

3. Final Answer:

   print("Hello", 10) -> Option D

4. Quick Check:

   No matching method for (String, int) call [OK]

Hint: Check parameter order and types carefully for overloaded methods [OK]

Common Mistakes:

• Assuming parameter order doesn't matter
• Thinking all combinations are allowed
• Ignoring method signature mismatch