Java 9 Try With Resource Enhancement

Java introduced try-with-resource feature in Java 7 that helps to close resource automatically after being used.

In other words, we can say that we don't need to close resources (file, connection, network etc) explicitly, try-with-resource close that automatically by using AutoClosable interface.

In Java 7, try-with-resources has a limitation that requires resource to declare locally within its block.

Example Java 7 Resource Declared within resource block

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
public class FinalVariable {
	public static void main(String[] args) throws FileNotFoundException {
		try(FileOutputStream fileStream=new FileOutputStream("javatpoint.txt");){
			 String greeting = "Welcome to javaTpoint.";    
		        byte b[] = greeting.getBytes();     
		        fileStream.write(b);    
		        System.out.println("File written");       	
		}catch(Exception e) {
			System.out.println(e);
		}		
	}
}

This code executes fine with Java 7 and even with Java 9 because Java maintains it's legacy.

But the below program would not work with Java 7 because we can't put resource declared outside the try-with-resource.

Java 7 Resource declared outside the resource block

If we do like the following code in Java 7, compiler generates an error message.

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
public class FinalVariable {
	public static void main(String[] args) throws FileNotFoundException {
		FileOutputStream fileStream=new FileOutputStream("javatpoint.txt");
		try(fileStream){
			 String greeting = "Welcome to javaTpoint.";    
		        byte b[] = greeting.getBytes();     
		        fileStream.write(b);    
		        System.out.println("File written");       	
		}catch(Exception e) {
			System.out.println(e);
		}		
	}
}

Output:

error: <identifier> expected
		   try(fileStream){

To deal with this error, try-with-resource is improved in Java 9 and now we can use reference of the resource that is not declared locally.

In this case, if we execute the above program using Java 9 compiler, it will execute nicely without any compile error.

Java 9 try-with-resource Example

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
public class FinalVariable {
	public static void main(String[] args) throws FileNotFoundException {
		FileOutputStream fileStream=new FileOutputStream("javatpoint.txt");
		try(fileStream){
			 String greeting = "Welcome to javaTpoint.";    
		        byte b[] = greeting.getBytes();     
		        fileStream.write(b);    
		        System.out.println("File written");       	
		}catch(Exception e) {
			System.out.println(e);
		}		
	}
}

Output: