Java 9.4.2 super Keyword Quiz

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Questions and Answers

How is the 'super' keyword used to refer to the immediate parent class instance variable?

It is used as 'super.variable_name'.

In Java, how is the 'super' keyword used to invoke an immediate parent class method?

It is used as 'super.method_name()'.

Explain how the 'super()' keyword is used in Java.

It is used to invoke the immediate parent class constructor.

In the given example, how is the color of the Animal class accessed in the Dog class's 'printColor' method?

By using 'super.color'. Signup and view all the answers

How is the 'super' keyword used to invoke a parent class method in the given example code?

By using 'super.method_name()'. Signup and view all the answers

What does the 'super.eat();' statement inside the 'work' method in TestSuper2 class achieve?

It calls the 'eat' method of the Animal class. Signup and view all the answers

What does the 'this' keyword refer to in Java?

The current object Signup and view all the answers

How can the 'this' keyword be used in Java?

To refer to current class instance variables, to invoke current class method (implicitly), and to invoke current class constructor. Signup and view all the answers

Give an example of using 'this' keyword to refer to current class instance variables in Java.

Student(int rollno, String name, float fee) { this.rollno=rollno; this.name=name; this.fee=fee; } Signup and view all the answers

How can you invoke the method of the current class using the 'this' keyword in Java?

By using the 'this' keyword. Signup and view all the answers

In which situations is the 'this' keyword not required in Java?

When referring to instance variables and invoking methods. Signup and view all the answers

What is the purpose of the 'this' keyword in Java?

To refer to the current object and to simplify referencing instance variables and methods within a class. Signup and view all the answers

What does the 'this' keyword do in Java when invoking a method?

It refers to the current class object. Signup and view all the answers

In Java, how can you call the default constructor from a parameterized constructor?

You use 'this();' to call the default constructor from a parameterized constructor. Signup and view all the answers

How can you call a parameterized constructor from a default constructor in Java?

You use 'this(parameters);' to call a parameterized constructor from a default constructor. Signup and view all the answers

What is the real usage of the 'this()' constructor call in Java?

The real usage is to reuse a constructor within another constructor. Signup and view all the answers

What is the super keyword used for in Java?

The super keyword is used to refer to the immediate parent class object. Signup and view all the answers

What is the purpose of the 'super' keyword in Java?

The purpose of the 'super' keyword is to call the parent class constructor or access parent class members. Signup and view all the answers

What happens if the `super()` keyword is not explicitly used in a subclass constructor?

A default <code>super()</code> is automatically added by the compiler to call the superclass constructor. Signup and view all the answers

In the given code snippet, what will be the output when the `main` method of `TestSuper3` class is executed?

The output will be: 'animal is created' followed by 'dog is created'. Signup and view all the answers

What is the purpose of using the `super(id, name)` in the `Emp` constructor of class `Emp`?

The <code>super(id, name)</code> is used to invoke the constructor of the superclass <code>Person</code> with the provided parameters. Signup and view all the answers

Explain the role of `this.id=id;` in the `Person` constructor.

<code>this.id=id;</code> assigns the value of the parameter <code>id</code> to the instance variable <code>id</code> of the current object. Signup and view all the answers

What will be the output when the `main` method of `TestSuper4` class is executed?

The output will be: 'dog is created'. Signup and view all the answers

What is the significance of the `super();` call in the `Dog` constructor of class `Dog`?

The <code>super();</code> call invokes the constructor of the superclass <code>Animal</code>, initializing the superclass before executing subclass-specific code. Signup and view all the answers

Study Notes

THIS Keyword in Java

this is a reference variable in Java that refers to the current object.
Usage of this:
- Refers to current class instance variables
- Invokes current class method (implicitly)
- Invokes current class constructor (this())

Using `this` to Refer to Current Class Instance Variables

Example: Student class uses this to refer to instance variables rollno, name, and fee.

Using `this` to Invoke Current Class Method

Example: A class uses this to invoke m() method from n() method.

Using `this` to Invoke Current Class Constructor

Example: A class uses this() to invoke default constructor from parameterized constructor.
Example: A class uses this() to invoke parameterized constructor from default constructor.

Real Usage of `this()` Constructor Call

Example: Student class uses this() to reuse constructor.

Super Keyword in Java

super is a reference variable that refers to the immediate parent class object.
Usage of super:
- Refers to immediate parent class instance variable
- Invokes immediate parent class method
- Invokes immediate parent class constructor

Using `super` to Refer to Immediate Parent Class Instance Variable

Example: Dog class uses super to refer to color variable of Animal class.

Using `super` to Invoke Immediate Parent Class Method

Example: Dog class uses super to invoke eat() method of Animal class.

Using `super` to Invoke Immediate Parent Class Constructor

Example: Dog class uses super() to invoke constructor of Animal class.
If no super() or this() is used, the compiler automatically adds it.

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Test your understanding of the Java 'super' keyword which is used to refer to the immediate parent class instance variable, method, or constructor when creating subclasses. Explore its usage in inheritance scenarios.

Java super Keyword

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Questions and Answers

How is the 'super' keyword used to refer to the immediate parent class instance variable?

In Java, how is the 'super' keyword used to invoke an immediate parent class method?

Explain how the 'super()' keyword is used in Java.

In the given example, how is the color of the Animal class accessed in the Dog class's 'printColor' method?

How is the 'super' keyword used to invoke a parent class method in the given example code?

What does the 'super.eat();' statement inside the 'work' method in TestSuper2 class achieve?

What does the 'this' keyword refer to in Java?

How can the 'this' keyword be used in Java?

Give an example of using 'this' keyword to refer to current class instance variables in Java.

How can you invoke the method of the current class using the 'this' keyword in Java?

In which situations is the 'this' keyword not required in Java?

What is the purpose of the 'this' keyword in Java?

What does the 'this' keyword do in Java when invoking a method?

In Java, how can you call the default constructor from a parameterized constructor?

How can you call a parameterized constructor from a default constructor in Java?

What is the real usage of the 'this()' constructor call in Java?

What is the super keyword used for in Java?

What is the purpose of the 'super' keyword in Java?

What happens if the super() keyword is not explicitly used in a subclass constructor?

In the given code snippet, what will be the output when the main method of TestSuper3 class is executed?

What is the purpose of using the super(id, name) in the Emp constructor of class Emp?

Explain the role of this.id=id; in the Person constructor.

What will be the output when the main method of TestSuper4 class is executed?

What is the significance of the super(); call in the Dog constructor of class Dog?

Study Notes

THIS Keyword in Java

Using this to Refer to Current Class Instance Variables

Using this to Invoke Current Class Method

Using this to Invoke Current Class Constructor

Real Usage of this() Constructor Call

Super Keyword in Java

Using super to Refer to Immediate Parent Class Instance Variable

Using super to Invoke Immediate Parent Class Method

Using super to Invoke Immediate Parent Class Constructor