Fundamentals of Java Programming

• A computer program is a sequence of instructions given to the computer in order to accomplish a specific task.
• Programming is the preparation and writing of programs for computers.
• Programmers write their programs in a high level programming language such as Java, C++, Python, Ruby or Scala.
• A Java compiler instead of translating Java code to machine language code, translates it into Java Bytecode (a highly optimized set of instructions)
• When the bytecode (also called a Java class file) is to be run on a computer, a Java interpreter, called the Java Virtual Machine (JVM), translates the bytecode into machine code and then executes it.
• The advantage of such an approach is that once a programmer has compiled a Java program into bytecode, it can be run on any platform (say Windows, Linux, or Mac) as long as it has a JVM running on it.
• To write a Java program, you will need a Text Editor (for writing the code) and a Java compiler (for compiling the code into bytecode).
• There are a wide variety of Java Integrated Development Environments (IDEs) available in the market that come equipped with a text editor and a Java compiler thus simplifying writing, compiling and executing Java programs.
• Most of them are freely downloadable from the Internet.
• We will be using the open source and free Java Net Beans IDE for writing Java programs.
• So let's dive straight in and write a simple Java program that prints a Welcome Message (“Hello World”) on the screen.
• Since this will be your first Java program, you will first need to setup the programming environment.
• An assertion is a mechanism for effectively identifying/detecting and correcting logical errors in a program.
• A multithreaded program is one that can perform multiple tasks concurrently so that there is optimal utilization of the computer's resources.
• The run() method is the entry point for every new thread that is instantiated from the class.
• Exceptions of the Exception type SQLException can occur while connecting or fetching data from the database and these can be caught using a try catch block.
• There are two ways to write an assertion assert expression; assert expression1 : expression2.
• An assert statement states a condition that should be true at a particular point during the execution of the program.
• To enable assertions at runtime, you can enable them from the command line by using the –ea option or in NetBeans, Right click on your project>Properties> Run>VMOptions and type–ea in the text box next to VM Options.
• An assert statement can be used to assert that the value of a variable should be greater than or equal to a certain value.
• The first statement in an assert expression evaluates expression and throws an AssertionError if expression is false.
• The first method to create a thread is to create a class that extends the Thread class from the java.lang package and override the run() method.
• The second statement in an assert expression evaluates expression1 and throws an AssertionError with expression2 as the error message if expression1 is false.
• In Java, threads can be created in two ways: by extending the Thread class or by implementing the Runnable interface.
• All software development in NetBeans is organized in the form of Projects, so we begin a new Project.
• There are 5 columns in the book table and they can be accessed using a for loop and the getString() method of the ResultSet object.
• In the IDE, click File> New Project (Ctrl + Shift + N) to create a new Java Application Project.
• It is good practice to make variable names meaningful.
• To assign a text value to a String variable we enclose the text between double quotes.
• Variable names written in capital letters differ from variable names with the same spelling but written in small letters.
• A variable of the primitive data type char can be used to store a single character.
• The + operator is used for addition, the - operator for subtraction, the * operator for multiplication, the / operator for division, the % operator for modulus, and the ==, !=, >, <, >=, <= operators for comparison.
• Java executes the instructions in sequential order, that is, one after the other.
• You can define multiple variables of the same type in one statement by separating each with a comma.
• In the Percentage Calculator program of the previous section, we used variables to store numeric data.
• Quite often we want variables to store textual data, for example, the name of a student.
• To store more than one character, we use the String class in Java.
• A program is nothing but a sequence of instructions.
• When used with Strings as operands, the + operator concatenates the strings together.
• To assign a value to a char variable we enclose the character between single quotes.