Java Identifiers and the rules

Rules for java identifiers

1 ) Characters that are allowed as java identifiers are

Alphabets : [ A – Z ] [ a – z ]

Digits : [ 0 – 9 ]

Special Charachters : [ $ or _ ]

If we are using any other character from the above-mentioned characters , we will get a Compile time exception .

package demo;

public class Demo {

  public static void main(String[] args) {

    String n@me = "Suraj";
  }
}

Output : Exception in thread "main" java.lang.Error: Unresolved compilation problems: Syntax error on token "@", ; expected me cannot be resolved to a variable

2 ) Java identifiers are case-sensitive . We can differentiate an identifier by changing the case .

package demo;

public class Demo {

  public static void main(String[] args) {

    String name = "Suraj";

    String Name = "Surya";

    System.out.println(name + "-" + Name);
  }
}

Output: Suraj - Surya

3 ) Java identifier cannot start with a digit . If we try to do that we will get a Compile time exception .

package demo;

public class Demo {

  public static void main(String[] args) {

    String 8name = "Suraj";
  }
}

Output : Exception in thread "main" java.lang.Error: Unresolved compilation problem: Syntax error on token "8", delete this token

4 ) We cannot use reserved keywords as identifiers else we will get a Compile time exception .

package demo;

public class Demo {

  public static void main(String[] args) {

    String for = "Suraj";
  }
}

Output: Exception in thread "main" java.lang.Error: Unresolved compilation problems: String cannot be resolved to a variable
Syntax error on token "for", delete this token

5 ) Identifier cannot have a space in the middle of words . If we do that we will get a compilation exception .

package demo;

public class Demo {

  public static void main(String[] args) {

    String my name = "Suraj";
  }
}

Output: Exception in thread "main" java.lang.Error: Unresolved compilation problems: Syntax error, insert ";" to complete BlockStatements name cannot be resolved to a variable

If we want to connect multiple words to form an identifier then we can use
_ ( underscore ) to connect them .

package demo;

public class Demo {

  public static void main(String[] args) {

    String my_name = "Suraj";

    System.out.println(my_name);
  }
}

Output: Suraj

6 ) All predefined java interface names and class names can be used as identifiers .

package demo;

public class Demo {

  public static void main(String[] args) {

    String String = "Suraj";

    System.out.println(String);
  }
}

Output: Suraj

Even though it is possible to use existing class and interface names as identifiers we should never do this because this is against java’s good programming practices .

7 ) There is no max length limit for java identifiers but it is suggested to keep the identifiers of smaller length .

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