How to fix "class, interface, or enum expected" error in Java

If you have ever written Java programs using Notepad or inside DOS editor, then you know that how a single curly brace can blow your program and throw 100s of error during compilation. I was one of those lucky people who started their programming on DOS editor, the blue window editor which allow you to write Java program. I didn't know about PATH, CLASSPATH, JDK, JVM, or JRE at that point. It's our lab computer where everything is supposed to work as much our instructor wants. Since we don't have the internet at that point of time, we either wait for the instructor to come and rescue us and we surprise how he solve the error by just putting one curly brace and all errors mysteriously go away.  Today, I am going to tell you about one such error,  "class, interface, or enum expected".   This is another compile time error in Java which arises due to curly braces. Typically this error occurs when there is an additional curly brace at the end of the program.

How to read a text file as String in Java

There was no easy way to read a text file as String in Java until JDK 7, which released NIO 2. This API now provides a couple of utility methods which you can use to read entire file as String e.g. Files.readAllBytes() returns a byte array of the entire text file. You can convert that byte array to String to have a whole text file as String inside your Java program. If you need all lines of files as List of String e.g. into an ArrayList, you can use Files.readAllLines() method. This return a List of String, where each String represents a single line of the file. Prior to these API changes, I used to use the BufferedReader and StringBuilder to read the entire text file as String. You iterate through the file, reading one line at a time using readLine() method and appending them into a StringBuilder until you reach the end of the file. You can still use this method if you are running on Java SE 6 or lower version.

Difference between a class and an interface in Java

It is one of the frequently asked Java questions from beginners which struggles to get the concept behind an interface. The main difference between a class and an interface lies in their usage and capabilities. An interface is the purest form of abstraction available in Java where you just define the API or contract e.g. you define run() method on the Runnable interface without worrying about how something will run, that is left to the implementor which will use a class to define how exactly to run. So an interface gives you method name but how the behavior of that method is come from the class which implements it. That's your general difference between an interface and class in Java and applicable to all object oriented programming language, not just Java. Even though this question is not exactly the difference between abstract class and interface, it's somewhat related to it because an abstract class is nothing but a class with some abstract method. The points I have discussed there, also applicable here in terms of rules of Java programming related to class and interface.