Programming in Java
Java is a programming language created by James Gosling from Sun Microsystems (Sun) in 1991.Oracle bought Sun, and thus they became the owners of Java.Java is open source, and you are free to use it.
Java program can be developed once and run on multiple operating systems. Java does not execute instructions on a computer directly, Instead it uses Java Virtual Machine (JVM).
Quick Q&A Session:
A Sample Java Program
In this example public, class, void, main are keyword, which we will learn shortly. Let us learn about main function and statements.
Main Function
Main function is from where the program execution begins. When you execute a program, Java starts your program by calling its main() function and executes statements, one by one. The syntax for the main function is as shown below.
Syntax for main function
public static void main(String args[]) {
// Code Execution Begins Here.
}
Printing Text in Java
System.out.println statement is used to print text in java and here is the syntax.
Syntax
System.out.println(" Your Text Here. ");
Example: Printing Text in Java
public class JavaProgram {
public static void main(String[] args) {
System.out.println(" My First Java Program. ");
}
}
Try it Yourself
Exercises
Exercise 1: Using two Statements
System.out.println(" Your Text Here. ");
System.out.println(" Your Second Text Here. ");
Do it Yourself
Please copy the two lines of above code and paste at main function in "Do it yourself" link.
Exercise 2: Using System.out.print
System.out.print(" Any Text Here. ");
System.out.print(" More Text in Same Line.");
Do it Yourself
Note: System.out.println prints next line after text. System.out.print doesn't, so any text follows is printed on the same line.
Compiling and Executing a Java Program
A compiler is a software that processes statements written in a particular programming language and turns them into machine language or "code" that a computer's processor understands. In java a program is converted to bytecode, the compiler creates a .class file.
A compile time error is an error that is detected by the compiler, while converting java program to bytecode. If there is a error, .class file will not be created.
Exercise: Find the syntax error in the following program:
public class JavaProgram {
public static void main(String[] args) {
System.out.println(" A Java Program.")
}
}
Find the output of the following program:
public class FindTheError {
public static void main(String[] args) {
System.out.println("My Name" "is John");
}
}
Simply use:System.out.println("My Name is John");
To join two strings, we learn shortly.
JVM
JVM (Java Virtual Machine) is a software. It is a specification that provides Runtime environment in which java bytecode can be executed.
Function of JVM
JVM mainly performs following operations.
- Allocating sufficient memory space for the class properties.
- Provides runtime environment in which java bytecode can be executed
- Converting byte code instruction into machine level instruction.
- JVM is separately available for every Operating System while installing java software so that JVM is platform dependent.
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Exercises
public class HelloWorld {
public static void main(String[] args) {
System.out.print("Hello ");
System.out.println("World");
}
}
World
System.out.println prints text in next line. System.out.print function is used to print text in the same line.