Table of Contents

• Classes and objects
  • Class Syntax
  • Defining a class
  • Creating an object
• Instance Fields
  • Defining instance Fields
  • Accessing instance Fields
• Methods
  • Defining a method
  • Invoking a method
• Conclusion

Classes are a very important concept in Java. Java code always needs to be written in a class. In this article, we will be taking a very close look at classes and understanding their syntax and semantics.

Classes and objects

A class defines a new data type. Once defined, this new type can be used to create objects of that type. So, a class acts like a template and provides the structure for an object.

Class Syntax

A class generally contains data and the code that operates on the data. The following is the general syntax of a class:

class classname{

	type var1;
	type var2;
	type varn;

type method1(parameters){
}

type method2(parameters){
}

type methodn(parameters){
}

}

The class keyword is followed by the name to be given to the class. The data in the class is present in the form of variables. These are known as instance fields. The code in the class is present in the form of methods. A class can contain any number of instance fields and methods. Also, both instance fields and methods are optional, a class can contain either instance fields or methods or both. Instance fields and methods are collectively referred to as members of a class.

class StudentDemo {

}

public class StudentDemo {

	public static void main(String[] args) {
		
		Student student1 = new Student();
	}

}

public class Student {
	
	String name;
	double marks;
	
}

Student student1 = new Student();
		
student1.name = "John Doe";
student1.marks = 93;

Student student2 = new Student();
		
student2.name = "Lucia Kane";
student2.marks = 78.5;

Methods

As mentioned earlier, a class can contain code in the form of methods. Methods generally operate on the data in the class.

public class Student {
	
	String name;
	double marks;
	
	void printDetails() {
		System.out.println("Student "+name+" has "+marks+" marks");
	}
	
}

Student student1 = new Student();
		
student1.name = "John Doe";
student1.marks = 93;
		
student1.printDetails();

Conclusion

So, just to summarise, a class acts like a template that can be used to create objects of the class. A class can contain instance fields and methods. In the next part of this article, we will be taking a closer look at methods and also exploring constructors.

The post Java Tutorial #7 Part 1 – Classes & Objects appeared first on Automation Dojos.

Table of Contents

• Introduction
• Break Statement
  • Break in a loop
  • Break in Switch statement
• Continue Statement
• Return Statement
• Conclusion

Introduction

The break statement is used to stop further execution. It can be used either in a loop or within a switch statement.

Break Statement

The break statement is used to stop further execution. It can be used either in a loop or within a switch statement.

int[] input = { 10, 20, 30,40,50 };

for (int num : input) {
if(num > 25) {
		break;
	}
System.out.println("Num:"+num);
}
System.out.println("Outside loop");

String dept = "IT";
switch(dept) {
case "HR": 
	System.out.println("Human Resources");
	break;
case "IT": 
	System.out.println("Information Technology");
	break;
case "Admin": 
	System.out.println("Administration");
	break;
default: 
	System.out.println("Invalid dept");
	break;
}
System.out.println("Outside switch");

If the break statement is not specified, then each case statement is checked even after a successful match.

int[] input = { 10, 20, 30,40,50 };

for (int num : input) {
if(num == 30) {
continue;
}
System.out.println("Num:"+num);
}
System.out.println("Outside loop");

Num:10
Num:20
Num:40
Num:50
Outside loop

public void greet() {
String greeting = sayHello("Earth");
	System.out.println(greeting);
}
	
public String sayHello(String name) {
return "Hello "+name;
}

Conclusion

Java jump statements help to transfer control to a different part of the code. The break statement terminates a loop and transfers control outside the loop. It can also be used to terminate a case statement in a switch block. The continue statement skips the current iteration of the loop, transfers control to the top of the loop and continues the next iteration. The return statement is used to return control from a method to an invoking method.

The post Java Tutorial #6 – Jump Statements appeared first on Automation Dojos.

Table of Contents

• While Statement
  • Syntax
  • Example
• Do-while Statement
  • Syntax
  • Example
• For Statement
  • Syntax
  • Example
• For-Each Statement
  • Syntax
  • Example
• Conclusion

Iteration statements are used to repeat a particular block of code until a certain condition is true. In this article, we will be taking a look at Java’s iteration statements.

While Statement

The while statement repeats a block of code as long as a condition is true.

while (condition){
//body of the loop
}

int i = 0;

while (i < 3) {
System.out.println("Loop Iteration: " + i);
	i++;
}
System.out.println("Done!");

Do-while Statement

A do-while loop is similar to a while loop except that it checks the condition at the end of the loop. This ensures that the body of the loop is executed at least once.

do{
// body of the loop
} while(condition);

int i = 0;

do {
System.out.println("Loop Iteration: " + i);
	i++;
} while (i < 3);
		
System.out.println("Done!");
This code is similar to the code above except that it uses a do-while loop. So, it produces the same output as before. 
However, consider the following code:
int i = 5;

do {
System.out.println("Loop Iteration: " + i);
	i++;
} while (i < 3);
		
System.out.println("Done!");

For Statement

A for loop can be used to iterate over a range of values. It continues the iteration until a condition is true, after which the loop is exited.

for(initialization;condition;iteration){
//body of the loop
}

for(int i = 0;i < 3;i++) {
System.out.println("Loop Iteration: " + i);
}
System.out.println("Done!");

For-Each Statement

The for-each loop is used to cycle through an array or a collection of objects.

for(datatype var : collection) {
//body of the loop
}

int[] input = { 10, 20, 30 };

for (int num : input) {
	System.out.println("Number is " + num);
}

Conclusion

Java iteration statements help to repeat a block of code. The while and do-while repeat a block of code as long as a condition is true. The do-while loop should be used when you want the body of the loop to be executed at least once. The for loop is used to iterate over a range of values. The for-each loop is used to iterate over an array or a collection.

The post Java Tutorial #5 – Loop Statements appeared first on Automation Dojos.

Table of Contents

• Introduction
• The ‘If’ Statement
  • Syntax
  • Basic If Statement
  • If-else Statement
  • Nested If Statement
• The Switch Statement
  • Syntax
  • Example
• Conclusion

Introduction

Control statements are used to change the flow of execution based on changes to certain variables in the code. One of the types of control statements are the selection statements or decision statements. These should be used when you want to check some condition and take a decision based on the condition. Java supports the if and switch statement decision statements

The ‘If’ Statement

The if statement is the most widely used control statement. It is used to check a condition. If the condition is true, it executes some code. You can also have an optional else part that executes if the condition is false. An if statement has the following syntax:

if(condition){
  //some code here
}
else { // this part is optional
    //some code here
}

Basic If Statement

The if statement can be used by itself, without having an else statement. In such a scenario, if the condition specified within the if statement is true, the code within the if block is executed after which control transfers outside the if block. If the condition in the if statement is false, the if block is not entered and control directly transfers outside the if block. The following code demonstrates this:

System.out.println("Enter a Value:");
Scanner scanner = new Scanner(System.in);
int i = scanner.nextInt();
if(i > 5) {
System.out.println("Value is greater than 5");
}
System.out.println("Outside if");
scanner.close();

Here, the if statement checks if the value entered by the user is greater than 5. If so, it executes a Sysout statement.  If the value entered by the user is less than 5, the if block is not entered. So, if the user enters the value 10, this code prints the following output:

Enter a Value:
10
Value is greater than 5
Outside if
If the user enters the value 2, this code prints the following output:
Enter a Value:
2
Outside if

If-else Statement

The else statement can also be used with the if statement. If the condition within the if statement is false, the code within the else block gets executed. The following code demonstrates this:

System.out.println("Enter a Value:");
Scanner scanner = new Scanner(System.in);
int i = scanner.nextInt();
if(i > 5) {
System.out.println("Value is greater than 5");
}
else {
	System.out.println("Value is less than 5");
}
scanner.close();

Here, the if statement checks if the value entered by the user is greater than 5. If so, it executes a Sysout statement, otherwise, it executes a different Sysout statement. So, if the user enters the value 10, this code prints the following output:

Enter a Value:
10
Value is greater than 5
If the user enters the value 2, this code prints the following output:
Enter a Value:
2
Value is less than 5

Nested If Statement

A nested if is simply an if statement within another if statement. Only if the outer if statement is true, the condition within the inner if statement is checked. Each if statement can have an optional else statement. The following code demonstrates this:

System.out.println("Enter a Value:");
Scanner scanner = new Scanner(System.in);
int i = scanner.nextInt();
if(i >= 5) {
if(i < 10) {
		System.out.println("Value is between 5 to 10");
	}
}
else {
	System.out.println("Value is less than 5");
}
scanner.close();

Here, the if statement checks if the value entered by the user is greater than or equal to 5. If so, there is another if statement within this if statement that checks if the value is less than 10. The inner if does not have an else statement while the outer if has an else statement. So, if the user enters the value 6, this code prints the following output:

Enter a Value:
6
Value is between 5 to 10
If the user enters the value 2, this code prints the following output:
Enter a Value:
2
Value is less than 5

The Switch Statement

Sometimes, you will need to write code that checks for several conditions. In such a scenario using multiple if-else statements makes the code difficult to read. Java provides the switch statement as an alternative. It checks a value and executes one of several code blocks based on the value. A switch statement has the following syntax:

switch(expression) {
		case value1: 
			//some code
			break; //optional
		case value2: 
			//some code
			break; //optional
		…..
case valuen: 
			//some code
			break; //optional

		default: 
			//some code
			break; //optional
		}
	}

System.out.println("Enter a Value:");
Scanner scanner = new Scanner(System.in);
int month = scanner.nextInt();
switch(month) {
case 1: 
	System.out.println("January");
	break;
case 2: 
	System.out.println("February");
	break;
case 3: 
	System.out.println("March");
	break;
//code for other months here
default: 
	System.out.println("Invalid month");
	break;
}
scanner.close();

Enter a Value:
2
February
If the user enters a value greater than 12, this code prints the following output:
Enter a Value:
14
Invalid month

Conclusion

Java decision statements help to execute code based on some conditions. Java has two main decision statements, if and switch. The if statement can have an optional else part. The switch statement can be used when you want to check for multiple values.

The post Java Tutorial #4 – Control Statements appeared first on Automation Dojos.

Table of Contents

• One Dimensional Array
  • Declaring Array
  • Allocting Memory to Array
  • Accessing Array Elements
  • Initializing Array
  • Length of Array
• Multi Dimensional Array
• Creating 3 Dimensional Array

Introduction

Arrays are used to store a group of values of the same data type. So a single variable can be used to refer to the group of values. Arrays can store data of any data type and can have one or more dimensions as explained below.

1. One-Dimensional Array

A one-dimensional array is essentially a list of values referred to by a common name.

int myArray[]; // creates myArray to store int values

myArray = new int[10]; // creates array of size 10

int myArray[] = new int[10]; //creates myArray with size 10

myArray[3] = 5; // element at index 3, i.e.4th element will be assigned 5

int value = myArray[2]; 
// value at index 2 i.e. 3rd position is assigned to the variable value

int myArray[] = {2,4,6,8,10}; 
//creates new array of size 5 with specified values

int myArray[] = {2,4,6,8,10};
int size = myArray.length; // size will be 5

2. Multi-Dimensional Arrays

Multidimensional arrays are basically arrays of arrays. They are used to store data in tabular form. Each additional index needs to be specified using additional square brackets.

int myArray[][] = new int[4][6];

int val = myArray[2][4]; 
// a will be assigned the element at row index 2 and column index 4

3. Creating and Using a 3-Dimensional Array

Similarly, you can create a 3-dimensional array as follows:

int myArray[][][] = new int [2][3][4];
myArray[1][0][3] = 5;

This code declares a 3-dimensional array with 2,3,4 as the dimensions. It sets the element at position 1,0,3 to 5.

Conclusion

So this article covers what arrays are and how you can use them. It also walks you through multi-dimensional arrays.

The post Java Tutorial #3 – Java Arrays appeared first on Automation Dojos.

Table of Contents

• Introduction
• 1. Assignment Operator
• 2. Arithmetic Operators
• 3. Compound Operators
• 4. Increment & Decrement Operators
• 5. Relational Operators
• 6. Logical Operators

Introduction

Operators are an essential part of any programming language. In-fact it is not possible not to write a decent piece of code without making use of ‘Operators’. Java operators can be categorized mainly into arithmetic, relational and logical operators. In addition, there is a special assignment operator that is used to assign values to variables. Each of these is covered in a separate section below.

1. Assignment Operator

The “=” sign is known as the assignment operator.  It assigns whatever is to its right to the variable on its left. The variable type must be compatible with the value being assigned. The following code demonstrates this:

int a = 10; //assigns the value 10 to the variable a

int b = 5+8; // assigns the value 13 to the variable b

2. Arithmetic Operators

Arithmetic operators are those that are used in ordinary mathematics, that is addition, subtraction, multiplication and division. These can only be applied to numerical operands. The Arithmetic operators can be further broken down into Basic Operators, Compound Assignment Operators and Increment/Decrement operators.

3. Compound Assignment

Java provides special operators which can be used to combine an operation with an assignment.  These are known as compound assignment operators. The compound operators are just shortcut operators which can be used when you want to change the value of a particular variable. Java supports compound assignment operators for each of the arithmetic operators as listed below:

4. Increment & Decrement Operators

Java provides two additional operators known as increment and decrement operators. These basically increment or decrement the variable on which they are invoked.

Both operators come in two variants, prefix and postfix. In the prefix form the operator precedes the operand and the operation is performed before the assignment. In the postfix form, the operator succeeds the operand and the operation is performed after the assignment. The following code demonstrates this:

int i = 5;
//postfix form, will print i, then increment, so will output 5
System.out.println(i++); 
int j = 10;
//prefix form, will decrement j first then print it, so will output 9
System.out.println(--j);

5. Relational Operators

Relational operators are used to determine the relationship between operands. They return a boolean value. Java has the following relationship operators:

6. Logical Operators

Logical operators operate on boolean values and are used to combine relational comparisons. Java has the following logical operators:

Logical operators can be used to combine relational comparisons as follows:

int a=30, b=20, c=10;
if(a > b && b > c){
// do something
}

The post Java Tutorial #2 – Operators in Java appeared first on Automation Dojos.

Table of Contents

• Introduction
• 1. Variables
• 2. Data Types
  • Primitive Data Types
    • Integer Data Types
    • Decimal Data Types
    • Character Data Types
    • Boolean Data Types
  • Reference Data Types

Introduction

Variables are names that are used to identify memory locations that store values. Each variable belongs to a particular data type. Data types determine the size of the memory location.In this article, we will be exploring Java variables and data types in detail.

1. Variables

A variable can be used to refer to a value at a memory location. The code can use and modify the value at the memory location using the variable.   A variable needs to be declared and initialized before it can be used.

int i; //declares a variable called i of int data type

int i,j,k; //declares 3 variables called i,j,k of int data type

int i = 100; // creates a variable i and sets it’s value to 100

int i; // declares int variable i
//do something else
i = 100; // sets i to 100

int sum = 10+6; //sets sum to 16
int sum2 = a+b; // adds the values in a and b and assigns the result to sum2

int a = b+27; // uses b in an expression
System.out.println(“a = “+a); // prints value of a
if(a > 20) { // uses a in an if statement
// do something
}

Conclusion

So this article covers declaring, initializing and using Java variables. It also walks you through the various data types supported by Java.

The post Java Tutorial #1 – Variables and Data Types appeared first on Automation Dojos.