In this section we are going to understand how to create a class and add attributes (variables) to it.

Creating class

We start with creating Person class. To start follow the steps given below:-

• Create a Text File.
• Rename the file as Person.java
• Use the text editor or an IDE to write the code
• Use keyword “class” to create a class.

    //creating the class.
    public class Person {
        
    }

Now the Person class is created but still it has no attributes or functionality, so now we will provide a set of attributes to it as variables.

Variables

• Every variable has a type
• Place the type first, followed by the name of the variable
• The semicolon is necessary because a declaration is a complete Java statement.
• A variable name must begin with a letter and must be a sequence of letters or digits.
• The length of a variable name is essentially unlimited.
• You can have multiple declarations on a single line.
• Names are highly case sensitive so variable newAccount is different from newaccount
• Local variables must be declared and initialized before use.

Initializing Variables

After you declare a variable, you must explicitly initialize it by means of an assignment statement—you can never use the values of uninitialized variables.

    public class RunnerClass {
    
        public static void main(String[] args) {
            int IntegerVariable;
            String StringVariable;
            
            System.out.println(IntegerVariable);
            System.out.println(StringVariable);
        }
    
    }

$ javac RunnerClass.java 
RunnerClass.java:7: error: variable IntegerVariable might not have been initialized
        System.out.println(IntegerVariable);
                           ^
RunnerClass.java:8: error: variable StringVariable might not have been initialized
        System.out.println(StringVariable);
                           ^
2 errors

To use a local variable, one must declare the variable before using it.

In Java you can put declarations anywhere in your code. For example, the following is valid code in Java:

• double salary = 65000.0;
• System.out.println(salary);
• int vacationDays = 12; // ok to declare a variable here

In Java, it is considered good style to declare variables as closely as possible to the point where they are first used.

    public class Main {
    
    	public static void main(String[] args) {
    		int IntegerVariable = 1;
    		String StringVariable = "Hello";
    		
    		System.out.println(IntegerVariable);
    		System.out.println(StringVariable);
    	}
    
    }

1
Hello

List of key words which cannot be used as variable names

Let’s return back to our Problem statement, since we have learned how to declare variables we will add variables to our Person class.

    //Adding variables to the class.
    public class Person {
        
        /* The will hold a string data type */
        private String firstName;
        
        /* The will hold a string data type */
        private String lastName;
        
        /* The will hold a string data type */
        private String accountNumber;
        
        /* The will hold a integer data type */
        private double balance;
        
    }

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