Java Keywords With Examples

A complete list of Java keywords are covered with examples in hopes that they will satisfy educational requirements.

Java Keywords List

As a result of Java keywords, there are a set of reserved words that can’t be used as variables, methods, classes, or any other identifiers:

Abstract Keyword In Java

In Java keywords, the abstract keyword acts as a non-access modifier for both classes and methods.

When talking abstract keyword in Java, these methods belong to the abstract class, and their bodies are empty.

Instead, the subclasses provide the body to it.

The following example shows the use of Abstract Method and Abstract Class in a more efficient way:

Similarly, To learn about abstract classes more clearly, refer to the given example:

Boolean Keyword In Java

Java Boolean keyword denotes a data type that can take only 2 types of values either true or false.

Usually, Boolean values are utilized for testing conditions.

Keep in mind when it comes to Java Keyword Boolean, the boolean data type has either true or false values.

The given code shows the use of boolean variables:

The following programme shows the views of people regarding America. The answers to their responses are given, creating the boolean variables using the boolean keyword:

Break Keyword In Java

As we are talking about Java keyword break, we are referring to the keyword that is used to break out of a loop like a for loop, while loop or switch block.

When the value of mrx equals 7, the loop should be terminated as follows:

Although the loop is assigned 100 cycles but because of the break keyword it stops the iteration when mrx becomes 7.

Similarly, the break keyword can also be used while traversing through a string array:

In the above example, despite the fact that the array contained 20 elements but because of the existence of the break keyword it did not print anything anymore when it reached the index number (8) of the Array.

We can also use the break keyword in a while loop.

The while loop is terminated when the value of mrx becomes 9:

Similarly, the break keyword in Java can also be used while traversing through an array.

As in the given example out of 10 teams,only 4 teams names are printed as the break keyword breaks the while loop when index (ample) reaches 4 (fifth element of the array american_Football_Club_Teams )

Byte Keyword In Java

With the byte keyword, you can store whole numbers between -128 and 127.

The given example shows the use of byte datatype to store a value of 89 to the the variable named mrx_Number;

Case Keyword In Java

When we talk about Java keyword Case, the keyword case traces a code block enclosed in a switch statement.

The following examples shows the use of Case Keyword :

Catch Keyword In Java

In the case of Catch Keyword in Java, the catch keyword captures the exceptions produced by try statements.

In case of an error in the try block, the catch statement executes a block of code.

Whenever an error occurs, you should use try-catch to catch the error and execute some code to deal with it in the following way:

Char Keyword In Java

Each character is stored in the char data type.

You must surround char values with single quotes, like ‘B’ or ‘e’.

Class Keyword In Java

When it comes to Java Keyword Classes, the class keyword generates a class.

Java requires every line of code to be inside a class.

There should always be an uppercase first letter in the class name, and the Java file name should be the same as the class name.

An object’s constructor is analogous to a class.

Below is an example of how it can be implemented in order to declare an object:

Correspondingly, it is possible to create as many classes as we want, by assigning different names to them:

In the example below, we declare an object of the MyFirstClass class and name it “mrx_Obj” which prints the value of ample (String):

Continue Keyword In Java

In the case of the keyword continue, while using a for loop (or a while loop), the continue keyword terminates the current iteration, and the next iteration proceeds.

In the case of mrx = 2, skip this iteration and continue with the next:

Using a while loop, we can also implement the continue keyword:

After the execution of the while loop you will notice that all numbers are printed except 4 which satisfies the working of continue keyword.

Correspondingly, We can also use the continue keyword while traversing through an array named : popular_Destination_Of_America:

Default Keyword In Java

When it comes to the keyword default in Java, the default keyword is the default block of code in a switch statement.

In the case that a switch does not match the case, the default keyword specifies some code to run.

In addition: In the case of the default keyword being used as the last statement in a switch block, you do not need to put a break keyword to it.

Here we have used 5 cases of the switch statement, hence upon entering 6 as the case value the default code is executed:

Correspondingly, the given example indicates if a number is even or odd :

Since, 11 % 2 = 1 (not 0) hence the default statement executes.

Do Keyword In Java

When it comes to Java Keyword Do, the do keyword is used together with the while keyword in order to generate a do-while loop.

In a while loop, a block of code is repeatedly executed until a specified condition is achieved.

A Do/while loop is an extension of the while loop.

In this loop, the code block will be executed once, before checking if the condition is true, and then the loop will be repeated if the condition is true.

Remember: Make sure the condition variable is increased, otherwise the loop will never terminate.

Despite the condition being false, the following loop will always run at least once since the code block is executed before the condition is evaluated:

This prints all the natural numbers from 1 to 4, as the condition is checked after printing the code.

The Given example shows the use of Do While Loop while traversing through the elements of the array:

As a result, all the elements of the array are printed because of prior printing of the elements than the condition.

Double Keyword In Java

The double keyword generates a double data type that is capable of holding decimal numbers within a range of 1.7 x 10^-308 to 1.7 x 10^308.

It is important to keep in mind that when specifying a value for the double data type, it should be suffixed with the letter “d”.

The following example shows how to print the value of a double variable (mrx):

Here we get the product of two double data type variables (mrx and ample):

Else Keyword In Java

The else keyword in Java is used in conjunction with an if statement to specify a block of code to be executed if the condition specified in the if statement is false.

In addition to the else statement, Java also offers other conditional statements such as:

1. The if statement, which is used to specify a block of code to be executed if a specified condition is true.
2. The else statement in Java is used to specify a block of code to be executed if the condition specified in the corresponding if statement is false. It allows for the execution of an alternative block of code in case the condition evaluated in the if statement is not met.
3. The else if statement, which is used to specify a new condition to test if the first condition is false.
4. The switch statement, which is used to specify multiple alternative blocks of code to be executed based on the value of an expression.

We can use the else if statement and assign it with a new testing condition in case the if condition gets false.

By using if else statements we can design a programme to calculate specific amounts of discounts at different ranges of bill as shown in the example below:

Correspondingly, the following program takes the time range as an string input and displays a message accordingly :

Enum Keyword In Java

While discussing the Java keyword enum, the enum keyword declares an enum (immutable) type.

An enum is a distinct “class” that symbolizes a collection of constants (unchangeable variables, similar to final variables).

Use the enum keyword to build groups of constants, separate them with commas, and make sure they are all uppercase.

The given example shows the creation of an enum named genders with non-modifiable values:

We can also create the enum of football field positions as shown below:

Enum vs Classes

Enums can have attributes and methods just like classes do. Enum constants are static, public, and final (i.e., they cannot be changed and cannot be overridden), this is the only property which makes them unique from the classes.

As enums are incapable of extending from other classes , hence object creation is impossible in them, on the contrary they can implement interfaces to perform respective operations.

You can implement enums while declaring values that will remain the same forever such as month days, days, colors, deck of cards, etc.

Extends Keyword In Java

When it comes to Ref Keyword Extends, the extends keyword expands a class (which indicates that a class is inherited from another class).

An attribute or method can be inherited from one class to the other in Java. As a result, we can classify the “inheritance concept” into two types:

A subclass (also known as a child class) – a class that has been inherited from another class

A superclass (also known as parent class) – this is the class from which we are inheriting

The extends keyword is used when you want to inherit from a class.

The given example shows the way to inherit methods and attributes to a child class from a parent class:

The following example shows the use of attributes and methods of the base class using the derived class object:

Final Keyword In Java

When it comes to Final Keyword in Java, it is not possible to inherit or override a class, attribute or method using this non-access modifier.

A variable that always stores the same value should be declared with the final keyword, such as the PI variable (3.14159).

The final keyword is also referred as a “modifier”.

To prevent a variable from being overridden or modified, set it to the final state:

Below given programme shows the modification of a variable that was made constant using the final keyword, hence upon execution an error will be generated:

Finally Keyword In Java

The finally keyword executes code regardless of whether there is an exception (used in try-catch statements).

Regardless of the outcome, they are responsible to run code after try-catch.

The try-catch is executed and the rest of the code can be executed from the next line

The given example shows the execution of the finally block even if the code generates an error in the try catch statement:

All indexes upto 4 from the Array are executed, and traversing array further generates an error

After executing the try-catch, we can continue with the rest of the code from here.

Float Keyword In Java

The float keyword used with a variable enables a special data type called float which can store fractional numbers that fall within the range 3.4e’038 to 3.4e+038.

It is important to note that you should end the value with an “f” or “F”:

The following programe shows the conversion of temperature from centigrade to Fahrenheit:

For Keyword In Java

Using the Java Keyword For, we can initialize a for loop that can iterate as many times as the condition is declared.

The following example shows the working of the for loop.

Here we print all the English language alphabets using their Ascii Codes:

Similarly, all the even numbers up to the user limit can be printed using the for loop as shown below:

From the example above:

• The first statement sets a variable before the loop begins (int ample = 0).
• The condition in statement 2 is that ample must be less than user_Input in order for the loop to run. The loop will restart if the condition is true, and it will end if it is false.
• The if condition checks the modulus of the number with respect to 2 if it shows 0, then it prints else it skips the iteration.
• Statement 3 increases a value (ample++) each time the code block in the loop has been executed.

A “for-each” loop is also available, which is primarily used to loop through the elements of an array one by one.

The following example shows the method of printing the names of top 6 brands of united states:

Below example shows the method of taking 5 names as an user input and printing them back with the help of for each loop:

If Keyword In Java

When it comes to Java Keyword If, the if statement indicates that a block of Java code will be executed if a certain condition is met.

The following conditional statements are available in Java:

1. If a condition is met, use if to execute a block of code.
2. In the case of a false condition, else is used to specify a block of code to execute.
3. When the first condition isn’t true, specify an else if condition to test instead.
4. Switches can be used to specify many alternative execution blocks.

Here we use string .equals() method to compare if two strings are exactly similar to each other or not:

Correspondingly, the following programme takes a sentence and a word as user input and shows if the word is the part of the sentence or not:

Test variables with the if statement:

The following program shows the output only if the mrx is greater than ample:

Similarly, if ample is greater than mrx we get the output otherwise nothing is printed:

When the condition is false, an else statement is used to specify a block of code that should be executed.

Considering the example we created above, here we use the else statement along with if to get outputs in both conditions (either condition is met or not) :

else if statements can be utilized to generate a new condition can be specified if the first condition isn’t true.

Here we use the else if condition to check if the numbers used in the examples above are equal:

The following programme shows the mechanism of working of an Atm machine using the java conditions and while loop:

Interface Keyword In Java

When talking about the Java Keyword Interface, the interface keyword is used to define a special type of abstract class that only comprises abstract methods.

When using an interface, its methods must be implemented by a class through the ‘implements‘ keyword, instead of ‘extends‘.

This class is responsible for providing the body of the given method.

The following example shows the working of interface keyword:

Similarly, following the example below we create another interface named My_Second_Interface:

Similarly, we can also create multiple interfaces in java:

Interfaces Key Points:

• It cannot be used to create objects (in the example above, it is not possible to create an “Mr_Examples” object in the Facts_and_Figures class).
• An interface method does not contain a body – its body is defined in the “implement” class.
• You must override all methods of an interface during implementation.
• In general, interface methods are abstract and public by default.
• By default, the attributes of an interface are public, static, and final.
• When it comes to Java keyword implements, there is no constructor in an interface (since an interface cannot create objects).

Interfaces Uses – Why And When?

In order to ensure security, certain details should be hidden or only shown when they are relevant to the operation of the object (interface).

It is not possible to inherit from more than one superclass in Java (each child class can have only one parent class).

Yet, with interfaces, this is possible, as a class can implement multiple interfaces when using the Java Keyword Implements.

Multiple Interfaces:

Another example shows the working phenomenon of multiple interfaces:

Import Keyword In Java

Packages, classes, and interfaces can be imported using the import keyword.

The Java API provides a ArrayList class, which can be imported as follows:

Similarly, we can also utilize the Scanner class from java.util package as shown below:

Instanceof Keyword In Java

While discussing Java Keyword Instanceof, instance of allows you to check if an object belongs to a certain class or interface.

When using the “instanceof” keyword, a boolean value of either true or false is given in exchange for comparing the instance with its particular type.

The example below shows its working:

Correspondingly, it shows the results as true when multiple objects are an instance of the Main class as shown below:

Int Keyword In Java

The int data type can hold integers ranging from -2147483648 to 2147483647.

Similarly, we can take two int inputs from the user and can find the modulus operator of them. For more clarification follow the example below:

Long Keyword In Java

The long data type is capable of storing whole numbers between -9223372036854775808 and 9223372036854775808.

Remember to end the value with an uppercase or lowercase “L”.

New Keyword In Java

Creating new objects is accomplished using the new keyword.

The following example shows the creation of an object using the new keyword:

Package Keyword In Java

Packages are created using the package keyword.

Firstly, we create a package named “myfirstpackage” using the keyword package:

Similarly, we can create another package using the package keyword:

Private Keyword In Java

An attribute, method, or constructor declared as private can only be accessed within the declared class using the private keyword.

The following example shows the use of private keyword inside a class:

Here, we create the private method and access it within the class using the object:

Protected Keyword In Java

Access modifiers such as protected make attributes, methods, and constructors accessible within packages or subclasses.

When it comes to Java Keyword Protected, here the User_Details subclass is capable of accessing a User class’s protected attributes such as:

Public Keyword In Java

When it comes to Keyword Public, the public keyword specifies an access modifier for classes, attributes, methods, and constructors, that makes them reachable by any other class.

Here we access multiple public attributes from one class to the other without extending the class:

Similar way can be utilized in order to access a method:

Return Keyword In Java

Return represents the end of the execution of a method, and can be used to return a value from a method after the execution has been completed.

The following method returns the product of 2 numbers:

The given programme take user input as an integer and calculates the factorial of it:

Such as: Factorial of 5 is: 5 * 4 * 3 * 2 * 1

Note: When void is used, the method does not have a return value.

The given example shows void methods that means that they do not have a return type:

Here is another example of using void method in order to divide variable mrx value by ample value:

Short Keyword In Java

In Java, the short keyword is the type of data type that can store whole numbers ranging from -32768 to 32767.

We can use a short variable if we want to store integers between -32768 to 32767:

Correspondingly, we can also find the sum of two short datatypes variables:

Static Keyword In Java

Static methods and attributes have a non-access modifier called static.

When using Java keyword static, static methods/attributes can be accessed without creating an object of the class.

In the example below we used the static attributes and accessed them without using the object:

Likewise, we can access the methods having static modifier without instantiating it with any object:

Super Keyword In Java

In the case of Java Keyword Super, super refers to superclass objects (parent class / base class).

In addition to accessing the superclass constructor, it is also intended to call superclass methods.

It is commonly used to avoid confusion between subclasses and superclasses that have the same method names.

A basic understanding of inheritance and polymorphism is required to understand the super keyword.

The following programme shows the use of super keyword() to access the methods of the parent class in child class method named information() :

We can also use a super() keyword to access a parent class constructor inside a child class constructor:

Switch Keyword In Java

When it comes to Java Keyword Switch, the switch keyword decides which one out of several code blocks to execute.

In the example below, it works as follows:

• Switch expressions are evaluated once.
• Each case’s value is compared with the expression’s value.
• When a match is found, the associated code block is executed.
• As soon as a match is found, the break keyword is used to terminate the switch block

We can learn how to use the switch statement by following the example below:

Here we can created a calculator in Java using switch case:

This Keyword In Java

When it comes to Java Keyword This, this refers to the object in a method or constructor.

This keyword is most commonly used to distinguish class attributes from parameters with the same name (due to the shadowing effect of a method or constructor parameter on a class attribute).

In the example below, without this keyword, the output would be “0” instead of “Java This keyword “.

In addition to this, it can also be used for:

• Call the constructor of the current class.
• Method of the current class is invoked.
• Get the object of the current class.
• When calling a method, pass an argument.
• Call the constructor with an argument.

Accessing a class attribute mrx with this keyword:

Throw Keyword In Java

When it comes to Ref Keyword Throw, the throw keyword generates a personalized error.

An exception type is used with the throw statement. ArithmeticException, ClassNotFoundException, ArrayIndexOutOfBoundsException, SecurityException, and so on are all exception types available in Java.

Like in the example below, exception types are often associated with custom methods.

Throw versus Throws

Throw:

• Method exceptions are thrown using this method.
• Exceptions can only be thrown once.

Throws:

• Indicates the type of exception that can be thrown by a method.
• It is possible to list multiple exceptions in Java Keyword Throw.

The following programme matches the number of digits as the ATM pin number entered by the user, and shows exception if the entered digits length is greater or less than 4:

And the following example shows the programme that takes two user inputs, compares them and shows an exception if they are not equal:

Throws Keyword In Java

The throws keyword specifies what exception types can be thrown by a method.

The exceptions thrown during this process are the same as what we discussed in the throw keyword.

From the example given above, we can clearly understand the working of the keyword throws:

Similarly, consider an array that contains 5 famous clothing brands of the United States. If we print more than the given number of brands it will generate an exception “ArrayIndexOutOfBoundsException” as shown below:

Try Keyword In Java

With reference to the Java keyword try, try-catch statement is produced.

You can use the try statement to test a block of code for errors while it is being executed.

Catch statements allow you to define a block of code that will be processed if the try block fails.

Try-catch is used to catch errors and then execute a piece of code to deal with them. Go through the examples below to understand its working more clearly:

The given example shows the exception if user enters data of other data types than int:

Void Keyword In Java

When we talk about Java Keyword Void, it specifies that a method with the void keyword should not return anything.

Similarly, the method in the example below does not return anything:

Corresponding, the following shows the working of a void method that takes user height in feet and converts it to feets:

The following programme returns 0 if the character is a vowel and 1 if it is a consonant and shows the results accordingly:

While Keyword In Java

When it comes to Java Keyword While, the while loop will loop through a block of code as long as a certain condition holds true.

Make sure to increase the variable assigned in the condition, otherwise the loop will never terminate.

The given examples shows all the even numbers starting from 0 to the user’s limit:

Correspondingly, the squares of numbers till the user’s limit can be calculated in the given way:

There is a variation of the while loop which can be referred to as the do/while loop. During the execution of this loop, the code block will be executed once, before it checks if the condition is true, and then it will repeat the loop as long as the condition is true:

The given example shows the sum of numbers up to the user’s limit by using the do/while loop:

Similarly, a while loop can be used to print the natural numbers up to the user limit: