Constructor chaining in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of constructor chaining with this()

What is the output of the following Java program that uses constructor chaining?

Java

public class Test {
    public Test() {
        this(5);
        System.out.print("A");
    }
    public Test(int x) {
        System.out.print("B");
    }
    public static void main(String[] args) {
        new Test();
    }
}

A BA

B AB

C A

D B

💡 Hint

Remember that this() calls another constructor before executing the current one.

The no-argument constructor calls the constructor with int parameter first, printing 'B'. Then it prints 'A'. So the output is 'BA'.

❓ Predict Output

intermediate

Constructor chaining with super() and this()

What will be printed when the following Java code runs?

Java

class Parent {
    Parent() {
        System.out.print("P");
    }
}
class Child extends Parent {
    Child() {
        this(10);
        System.out.print("C");
    }
    Child(int x) {
        super();
        System.out.print("X");
    }
}
public class Main {
    public static void main(String[] args) {
        new Child();
    }
}

A XP

B PCX

C PC

D PXC

💡 Hint

Check the order of constructor calls: this() calls another constructor, which calls super().

Child() calls this(10), which calls super() printing 'P', then prints 'X'. After returning, Child() prints 'C'. So output is 'PXC'.

🔧 Debug

advanced

Identify the compilation error in constructor chaining

Which option correctly identifies the compilation error in this Java class?

Java

public class Demo {
    Demo() {
        this(5);
        System.out.println("Hello");
    }
    Demo(int x) {
        this();
        System.out.println(x);
    }
}

A Cannot call this() and super() in the same constructor

B Missing return statement in constructor

C Recursive constructor call causing a compile-time error

D No default constructor defined

💡 Hint

Check if constructors call each other in a loop.

The constructor Demo() calls Demo(int), which calls Demo() again, causing infinite recursion in constructor calls. This is a compile-time error.

📝 Syntax

advanced

Which constructor chaining syntax is invalid?

Which of the following constructor chaining statements will cause a compilation error in Java?

A public MyClass() { super(); this(10); }

B public MyClass() { this(10); }

C public MyClass(int x) { super(); }

D public MyClass(int x) { this(); }

💡 Hint

Remember that this() or super() must be the first statement in a constructor.

In option A, super() is called first, then this(10), which is invalid because this() or super() must be the first statement and only one can be called.

🚀 Application

expert

Number of times constructors are called in chaining

Given the following Java classes, how many times is the constructor of class A called when creating new C()?

Java

class A {
    A() {
        System.out.print("A");
    }
}
class B extends A {
    B() {
        this(5);
        System.out.print("B");
    }
    B(int x) {
        super();
        System.out.print(x);
    }
}
class C extends B {
    C() {
        super();
        System.out.print("C");
    }
}
public class Main {
    public static void main(String[] args) {
        new C();
    }
}

A 0

B 1

C 3

D 2

💡 Hint

Trace constructor calls from C() up to A(), count how many times A() runs.

Creating new C() calls C(), which calls B() no-arg, which calls B(int) via this(5). B(int) calls super() which calls A() once. So A() is called once.