Constructor execution flow in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call the parent class constructor from the child class.

Java

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

class Child extends Parent {
    Child() {
        [1];
        System.out.println("Child constructor");
    }
}

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

Asuper()

Bthis()

CParent()

Dparent()

Attempts:

3 left

💡 Hint

Common Mistakes

Using this() instead of super()

Calling Parent() like a method

Forgetting to call the parent constructor

In Java, super() calls the parent class constructor.

2fill in blank

medium

Complete the code to call another constructor in the same class.

Java

class Example {
    Example() {
        this(10);
        System.out.println("Default constructor");
    }

    Example(int x) {
        System.out.println("Constructor with value: " + [1]);
    }
}

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A10

Bthis

Cx

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using this instead of the parameter name

Using the literal 10 instead of the parameter

Using an undefined variable

The parameter name x is used to print the passed value.

3fill in blank

hard

Fix the error in the constructor chaining code.

Java

class Test {
    Test() {
        [1];
        System.out.println("No-arg constructor");
    }

    Test(int a) {
        System.out.println("Constructor with int: " + a);
    }
}

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Athis(5)

Bthis()

CTest(5)

Dsuper(5)

Attempts:

3 left

💡 Hint

Common Mistakes

Using super(5) when no parent constructor with int exists

Calling Test(5) like a method

Using this() which calls no-arg constructor causing recursion

Use this(5) to call another constructor in the same class with an int argument.

4fill in blank

hard

Fill both blanks to complete the constructor chaining and print the correct messages.

Java

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

class Derived extends Base {
    Derived() {
        [1];
        System.out.println("Derived constructor");
    }

    Derived(int x) {
        System.out.println("Derived with int: " + [2]);
    }
}

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Athis(5)

Bsuper()

Cx

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using super() instead of this(5) in the no-arg constructor

Printing the literal 5 instead of the parameter x

Not chaining constructors properly

The no-arg constructor calls this(5) to chain to the int constructor, which prints the parameter x.

5fill in blank

hard

Fill all three blanks to create a class with constructor chaining and parent constructor call.

Java

class Alpha {
    Alpha() {
        System.out.println("Alpha default");
    }

    Alpha(String msg) {
        System.out.println(msg);
    }
}

class Beta extends Alpha {
    Beta() {
        [1];
        System.out.println("Beta default");
    }

    Beta(String msg) {
        [2];
        System.out.println("Beta with message: " + [3]);
    }
}

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Athis("Hello")

Bsuper(msg)

Cmsg

Dsuper()

Attempts:

3 left

💡 Hint

Common Mistakes

Calling super() instead of this() in the no-arg constructor

Not calling super(msg) in the string constructor

Printing a variable not defined or the wrong variable

The no-arg constructor calls this("Hello") to chain to the string constructor.
The string constructor calls super(msg) to call the parent constructor with the message.
Finally, it prints the message using the parameter msg.