Constructor execution flow in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this constructor execution?

Consider the following Java code with inheritance and constructors. What will be printed when new Child() is executed?

Java

class Parent {
    Parent() {
        System.out.println("Parent constructor");
    }
}

class Child extends Parent {
    Child() {
        System.out.println("Child constructor");
    }
}

public class Test {
    public static void main(String[] args) {
        new Child();
    }
}

A

Parent constructor
Child constructor

B

Child constructor
Parent constructor

C Child constructor

D Parent constructor

💡 Hint

Remember that the parent constructor runs before the child constructor.

When creating a Child object, Java first calls the Parent constructor implicitly, then the Child constructor. So the output is Parent constructor followed by Child constructor.

❓ Predict Output

intermediate

What is the output when constructors call each other?

Analyze the constructor calls and determine the output.

Java

class A {
    A() {
        this(5);
        System.out.println("A no-arg");
    }
    A(int x) {
        System.out.println("A int: " + x);
    }
}

public class Test {
    public static void main(String[] args) {
        new A();
    }
}

A

A no-arg
A int: 5

B

A int: 5
A no-arg

C A int: 5

D Compilation error

💡 Hint

Look at how this() calls another constructor before printing.

The no-argument constructor calls the one-argument constructor first, which prints A int: 5. After that finishes, it prints A no-arg.

🔧 Debug

advanced

What error occurs in this constructor chaining?

Examine the code and identify the error that occurs when compiling.

Java

class B {
    B() {
        this();
        System.out.println("B no-arg");
    }
}

public class Test {
    public static void main(String[] args) {
        new B();
    }
}

A NullPointerException at runtime

B StackOverflowError at runtime

C No output, program runs silently

D Compilation error: recursive constructor call

💡 Hint

Check how this() is used inside the constructor.

The constructor calls itself recursively with this() without a base case, causing a compile-time error for recursive constructor invocation.

❓ Predict Output

advanced

What is the output of this multi-level constructor chain?

Given the classes below, what will be printed when new C() is executed?

Java

class A {
    A() {
        System.out.println("A constructor");
    }
}

class B extends A {
    B() {
        System.out.println("B constructor");
    }
}

class C extends B {
    C() {
        super();
        System.out.println("C constructor");
    }
}

public class Test {
    public static void main(String[] args) {
        new C();
    }
}

A

A constructor
B constructor
C constructor

B

B constructor
A constructor
C constructor

C Compilation error

D

A constructor
C constructor
B constructor

💡 Hint

Remember the order of constructor calls in inheritance.

When C() is called, it calls B() via super(), which implicitly calls A(). So the order is A, then B, then C.

🧠 Conceptual

expert

How many times is the constructor of class A called?

Consider the following code. How many times is the constructor of class A executed when new D() is called?

Java

class A {
    A() {
        System.out.println("A constructor");
    }
}

class B extends A {
    B() {
        System.out.println("B constructor");
    }
}

class C extends A {
    C() {
        System.out.println("C constructor");
    }
}

class D extends B {
    D() {
        super();
        System.out.println("D constructor");
    }
}

public class Test {
    public static void main(String[] args) {
        new D();
    }
}

A 2

B 3

C 1

D 0

💡 Hint

Trace the inheritance chain and constructor calls carefully.

Class D extends B, which extends A. When D() is called, it calls B(), which calls A(). Class C is unrelated here and its constructor is not called. So A() runs once.