Dive into the intricate world of Java programming language with a focus on the Java This Keyword. This comprehensive guide explores the definition, essential features and efficient ways to use this keyword in Java. From practical examples to its key functions and roles, you can expect to gain an in-depth understanding. Additionally, the guide sheds light upon the Super Keyword in Java, the differences between this and super keyword, when to use them, and much more. This is the ideal resource for advancing your Computer Science knowledge and skills, especially in the realm of Java.
Understanding Java This Keyword
Aspiring to break into the world of programming, you might encounter the Java programming language and a special keyword called 'this'. The keyword 'this' in Java can be initially perplexing, but with a bit of understanding, you'll find it to be a handy tool in your coding toolkit.
Defining What is This Keyword in Java
The 'this' keyword in Java is a reference variable that refers to the current object. In simpler words, it signifies the instance of the class where it is used.
It often comes in handy in situations where you need to distinguish between class attributes and parameters with the same name.
Essential Features of This Keyword in Java
Here are some crucial features of the 'this' keyword in Java:
- It can be used to refer to the current class instance variable.
- It can be used to invoke the current class method.
- It can be used to invoke the current class constructor.
- And it can also be passed as an argument in the method call.
Efficient Ways to Use This Keyword in Java
When used efficiently, 'this' keyword in Java can make your code cleaner and more readable. For example, it eliminates the confusion when class attributes and parameters bear the same name.
Suppose you have a class 'Student' with a method 'setAge(int age)', where age is a class attribute and a method parameter. Without 'this', there's a naming conflict:
class Student {
int age;
void setAge(int age) {
age = age;
}
}
By using 'this', you can resolve this conflict:
class Student {
int age;
void setAge(int age) {
this.age = age;
}
}
Practical Example of This Keyword in Java
Let's illustrate this with a practical example. Consider a 'Person' class with name, age and weight as attributes. You will use 'this' keyword to differentiate between class attributes and constructor parameters as follows:
class Person {
String name;
int age;
double weight;
Person(String name, int age, double weight) {
this.name = name;
this.age = age;
this.weight = weight;
}
}
In Java, This Keyword is Used To: Key Functions and Roles
While 'this' keyword is mainly used to differentiate between class attributes and parameters, its usages do not stop there in Java.
Let's examine the key functions and roles of 'this' keyword in Java:
- 'this' can be used to call an overloaded constructor in the same class.
- 'this' can be used to pass itself to another method or constructor.
- 'this' can be used to return the current class instance from the method.
Examining the Java This Keyword Usage in More Detail
'Java This Keyword' comes of great use in various situations. One of those is when it's used within an instance method or a constructor, this keyword is a reference to the current object — the object whose method or constructor is being called. You can refer to any member of the current object from within an instance method or a constructor by using this keyword.
Here's an example to illustrate how 'this' keyword is used in a method to refer to the current object.
class Vehicle {
int maxSpeed;
Vehicle(int maxSpeed) {
this.maxSpeed = maxSpeed;
}
void display() {
System.out.println("Max speed: " + this.maxSpeed);
}
}
In this example, 'this' refers to the current object in the display() method.
Exploring the Java Super Keyword
As you delve deeper into the expansive world of Java, another keyword that you'll often encounter alongside 'this' is 'super'. The 'super' keyword also holds a significant place in Java syntax and programming, and understanding its usage and benefits is essential. It is a reference variable that helps to refer to the immediate parent class object. Each time you create an instance of a class, the 'super' keyword is created as a symbol of the parent class.
Understanding This and Super Keyword in Java
Both 'this' and 'super' keywords have their own unique functionalities, and both serve different purposes, though they are often confused because of their somewhat related usages.
While 'this' refers to the current class object, 'super' refers to the parent class object. They are used to access methods and variables of the current class or the parent class respectively.
Let's break down the functions of 'super' in Java for better understanding:
- 'Super' can be used to refer to immediate parent class variable.
- 'Super' can be used to invoke immediate parent class method.
- 'Super()' is used to invoke immediate parent class constructor.
Recognising the Importance of Super Keyword in Java
Understanding the importance of 'super' in Java is pivotal. The use of 'super' becomes necessary when sub-classes contain methods or variables that are also present in their parent class. In such a scenario, if you wish to access the method or variable of the parent class, 'super' keyword comes into play.
Furthermore, 'super' is also used to invoke the constructor of the parent class, which can be extremely useful when working with inheritance, one of Java's fundamental principles.
Inheritance in Java is a mechanism where one object acquires all the properties and behaviours of the parent object. It’s an important part of OOPs (Object Oriented programming system).
Comprehensive Example of Java Super Keyword
Diving into a comprehensive example can help put all this theory into perspective. Let's consider that a class 'Animal' has a method 'eat()'. Another class 'Dog' extends 'Animal' and overrides the 'eat()' method.
Here's how you can use the 'super' keyword to call the parent class 'Animal' method 'eat()' from the child class 'Dog':
class Animal {
void eat() {
System.out.println("Animal is eating...");
}
}
class Dog extends Animal {
void eat() {
super.eat();
System.out.println("Dog is eating...");
}
}
Super Keyword: Applying it within Java Code
One more example can solidify your understanding of the application of 'super' keyword within Java code. Consider two classes — 'Parent' and 'Child', where 'Child' class extends 'Parent'. Both classes have a variable 'x' and a method 'display()'.
class Parent {
int x = 10;
void display() {
System.out.println("Parent's x: " + x);
}
}
class Child extends Parent {
int x = 20;
void display() {
super.display();
System.out.println("Child's x: " + x);
}
}
In the child class, 'super.display()' invokes the display() method of the parent class, which will print the value of 'x' of the parent class. The second line will print the value of 'x' in the child class. This is an example of how 'super' can be used to avoid variable hiding in Java.
Distinguishing Between This and Super Keyword in Java
Java, like other object-oriented
programming languages, includes the 'this' and 'super' keywords. Both carry unique implications and are used under different circumstances. 'This' refers to the current object, whereas 'super' points to the immediate parent class object. Discerning them is crucial to avoiding errors and ensuring smooth execution of Java code.
Fundamental Difference between This and Super Keyword in Java
The 'this' and 'super' keywords possess distinctive functionalities within the scope of Java programming language:
'This' keyword, in its essence, refers to the current class instance. It is utilised within a method or constructor to refer to the current object. It aids in accessing the current class's methods and variables, and differentiating between instance variables and parameters when both share identical names.
On the other hand,
'Super' keyword, as opposed to 'this', is used to access methods and variables of the immediate parent class. When a class inherits another, 'super' can be used to point to the superclass. This becomes particularly useful when a child class wants to call a method or access a variable from the parent class.
Understanding the divergence between 'this' and 'super' is imperative in tackling inheritance related tasks, overloading, and avoiding ambiguity between variable names.
How to Identify This and Super Keyword in Java
To identify 'this' keyword in Java, you need to notice its usage within class methods and constructors. It's usually used when variable names are repeated in a method's parameter and class's instance variable.
For instance, in the following class 'Employee', 'this' keyword is used to clearly differentiate between class variable 'id' and method parameter 'id'.
class Employee {
int id;
void setId(int id) {
this.id = id;
}
}
Identifying 'super' keyword hinges on its application in child classes. Since Java supports inheritance, 'super' benefits from accessing the superclass methods or variables within the subclass.
A typical example of 'super' usage can be seen in the following class 'Rectangle', which is a subclass of 'Shape'. 'Super' accesses the parent class method 'area()'.
class Shape {
void area() {
//calculate area
}
}
class Rectangle extends Shape{
void area() {
super.area();
//calculate rectangle area
}
}
When to Use This Keyword and Super Keyword in Java Programming
Deciding when to invoke 'this' or 'super' is down to requirement and circumstance. Typically, you exploit 'this' keyword in scenarios, where there is a need to distinguish between instance variables and parameters with identical names. It's also helpful when invoking one constructor from another within the same class.
Conversely, you use the 'super' keyword when you want to invoke overridden methods in the parent class or call a parent class's constructor. It helps preserve the concept of inheritance by accessing the superclass from the subclass.
An example would be a 'Vehicle' class having 'speed' as a property and a 'Car' class that extends 'Vehicle' with an additional 'engine' property. When creating a new car, you would use 'super' to call the constructor of 'Vehicle' and 'this' would be used to refer to 'Car' properties.
class Vehicle {
int speed;
Vehicle(int speed) {
this.speed = speed;
}
}
class Car extends Vehicle {
String engine;
Car(int speed, String engine) {
super(speed);
this.engine = engine;
}
}
Java This Keyword - Key takeaways
- Java This Keyword: A reference variable that points to the current object.
- Essential Features of This Keyword: Can be used to refer to the current class instance variable, invoke current class method, invoke current class constructor and passed as an argument in method call.
- Java Super Keyword: A reference variable used to refer to the immediate parent class object.
- This vs Super in Java: 'This' refers to the current class object while 'super' refers to the immediate parent class object. Both are used to access methods and variables of the current class and parent class respectively.
- Proper usage of 'this' and 'super' is crucial for avoiding errors, ambiguity in variable names, and for smooth execution of Java code.
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