Java Basics
First program in java
/* This is a simple Java program.
Call this file "Example.java".
*/
class Example {
// Your program begins with a call to main().
public static void main(String args[]) {
System.out.println("This is a simple Java program.");
}//End of main
}//End of class
Compiling java program
C:\>javac Example.java
Run java program
c:/java Example
Datatypes:
byte, short, int, long, char, float, double
Scope and Lifetime of Variables
int x=10;
if(x==10)
int y = 20;
System.out.println("x and y: " + x + " " + y); // x and y both known here.
x = y * 2;
}
y = 100; // Error! y not known here
This program will not compile
class ScopeErr {
public static void main(String args[]) {
int bar = 1;
{
// creates a new scope
int bar = 2; //Possible in c++
// Compile-time error – bar already defined!
}
}
}
Type Conversion
// Demonstrate casts.
class Conversion {
public static void main(String args[]) {
byte b;
int i = 257;
double d = 323.142;
System.out.println("\nConversion of int to byte.");
b = (byte) i;
System.out.println("i and b " + i + " " + b);
System.out.println("\nConversion of double to int.");
i = (int) d;
System.out.println("d and i " + d + " " + i);
System.out.println("\nConversion of double to byte.");
b = (byte) d; System.out.println("d and b " + d + " " + b);
}
}
Type Promotion
byte b = 50;
b = b * 2; // Error! Cannot assign an int to a byte!
byte b = 50;
b = (byte)(b * 2);//correct value of 100.
Operators
- Assignment( = )
- Arithmetic Ex.(+, -, *, /, %)
- Relational(<, >, <=, >=, ==)
- Logical(&&, ||, !)
- Increment and Decrement (++, --)
- Ternary ( ?: )
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