Identifier Expected Error in Java

1. Understanding <identifier> expected Error in Java
2. Example 1: When Parameters in a Method Are Missing Data Type or Name
3. Example 2: When the Expression Statements Are Misplaced
4. Example 3: When Declaration Statements Are Misplaced
5. Conclusion

In this article, we will learn about Java’s <identifier> expected error.

Understanding <identifier> expected Error in Java

The <identifier> expected is the most common Java compile-time error faced by novice programmers. This error occurs when a method parameter does not have a data type or name declared or when an expression statement is written outside a method, a constructor, or an initialization block.

In Java, an identifier is a sequence of one or more characters where the 1st character must be a letter or $ or _, and the subsequent characters can be letters, digits, $ or _.

These identifiers are used to name a variable, a method, a class, a package, an interface, etc.

When the Java code is compiled initial phase involves lexical analysis of the program. Here the program is categorized into tokens, and all the tokens, including identifiers, are verified against a set of grammar rules.

And whenever as per grammar rules, an identifier is expected, but it’s not present, and something else is found in its place compiler raises the <identifier> expected error. Angle brackets here signify a reference to the token objects.

Let’s look at some examples to understand it better now.

Example 1: When Parameters in a Method Are Missing Data Type or Name

Parameters inside a method must have data followed by the variable name, which is an identifier; missing either of those will inevitably raise the <identifier> expected error.

1. Data of the parameter is missing

   public class Demo {
     public static int square(x) {
       return x * x;
     }
   
     public static void main(String[] args) {
       System.out.println(square(10));
     }
   }
   

   Output:

   square.java:9: error: <identifier> expected
   public static int square(x) {
           	        	  ^
   1 error
   

   If we observe the error above, we see that variable x is missing the data type. If we give the data type for it, it will work properly.

   public class Demo {
     public static int square(int x) {
       return x * x;
     }
   
     public static void main(String[] args) {
       System.out.println(square(10));
     }
   }
   

   Output:

   100
   

2. The parameter’s data type is the identifier; the variable name is missing here.

   public class Demo {
     public static int square(int) {
       return x * x;
     }
   
     public static void main(String[] args) {
       System.out.println(square(10));
     }
   }
   

   Output:

   square.java:9: error: <identifier> expected
   public static int square(int) {
           	        	   ^
   1 error
   

   If we observe the error above, we can clearly see that we specified the data type but didn’t attach any variable name.

   public class Demo {
     public static int square(int x) {
       return x * x;
     }
   
     public static void main(String[] args) {
       System.out.println(square(10));
     }
   }
   

   Output:

   100
   

Example 2: When the Expression Statements Are Misplaced

The compiler raises an error when an expression statement is written outside a method, a constructor or an initialization block <identifier> expected.

Example code:

public class Demo {
  private String name;
  name = "Naruto";
  System.out.println(name);
}

Output:

Demo.java:9: error: <identifier> expected
  name = "Naruto";
      ^
Demo.java:10: error: <identifier> expected
  System.out.println(name);
                    ^
Demo.java:10: error: <identifier> expected
  System.out.println(name);
                        ^
3 errors

If we observe the error above, the error occurs because the statements are not enclosed within a function or a constructor. Let’s write these statements inside a method named print.

public class Demo {
  private String name;

  public void print() {
    name = "Naruto";
    System.out.println(name);
  }

  public static void main(String[] args) {
    Demo obj = new Demo();
    obj.print();
  }
}

Output:

Naruto

Example 3: When Declaration Statements Are Misplaced

This is rare but not unheard of when working with try-with-resources statements. All these statements require that any closable resource be declared immediately after the try keyword.

If the resource variable is declared outside the try-with-resources statement, then the <identifier> expected error might be raised by the compiler (as compiler to compiler, this may vary).

Example code: Here, the closable resource is BufferedReader.

import java.io.*;

public class Demo {
  public static void main(String[] args) {
    StringBuilder obj = new StringBuilder();
    BufferedReader br = null;

    try (br = new BufferedReader(new InputStreamReader(System.in))) {
      String lines = "";
      while (!(lines = br.readLine()).isBlank()) {
        obj.append(lines);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

Output:

Demo.java:13: error: <identifier> expected
        try (br = new BufferedReader(new InputStreamReader(System.in))) {
              ^
1 error

The error will be resolved if we declare the BufferedReader obj inside the try block.

import java.io.*;

public class Demo {
  public static void main(String[] args) {
    StringBuilder obj = new StringBuilder();

    try (BufferedReader br = new BufferedReader(new InputStreamReader(System.in))) {
      String lines = "";
      while (!(lines = br.readLine()).isBlank()) {
        obj.append(lines);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

Conclusion

In this article, we learned about why the <identifier> expected error had been raised by the compiler and how it’s the most common compile-time error faced by newbies. We also looked at different examples analyzing the cases when this error was raised.