Java

Java became popular quickly. With the advent of Java 2, new versions had multiple configurations built for different types of platforms. For example, J2EE was for enterprise applications and the greatly stripped down version J2ME was for mobile applications. J2SE was the designation for the Standard Edition. In 2006, for marketing purposes, new J2 versions were renamed Java EE, Java ME, and Java SE, respectively.
In 1997, Sun Microsystems approached the ISO/IEC JTC1 standards body and later the Ecma International to formalize Java, but it soon withdrew from the process. Java remains a de facto standard that is controlled through the Java Community Process. At one time, Sun made most of its Java implementations available without charge although they were closed source, proprietary software. Sun's revenue from Java was generated by the selling of licenses for specialized products such as the Java Enterprise System. Sun distinguishes between its Software Development Kit (SDK) and Runtime Environment (JRE) which is a subset of the SDK, the primary distinction being that in the JRE, the compiler, utility programs, and many necessary header files are not present.

        Rounding errors occur when an exact conversion between numbers is not possible
    double f = 4.35;
    System.out.println(100 * f); // prints 434.99999999999994
        Java: Illegal to assign a floating-point expression to an integer variable
    double balance = 13.75;
    int dollars = balance; // Error
       Casts: used to convert a value to a different type
    int dollars = (int) balance; // OK
       Cast discards fractional part.
    Math.round converts a floating-point number to nearest integer
    long rounded = Math.round(balance); // if balance is 13.75,
                                    // rounded is set to 14

String

The String class represents character strings. All string literals in Java programs, such as "abc", are implemented as instances of this class.
Strings are constant; their values cannot be changed after they are created. String buffers support mutable strings.
Because String objects are immutable they can be shared. For example:

     String str = "abc";

is equivalent to:

     char data[] = {'a', 'b', 'c'};
     String str = new String(data);

Here are some more examples of how strings can be used:

System.out.println("abc");
String cde = "cde";
System.out.println("abc" + cde);
String c = "abc".substring(2,3);
String d = cde.substring(1, 2);

Occasionally you may want to perform some actions for the false outcome of the condition as well. The else keyword is used to separate branches.

Caution: For loops can be written in ways that violate structured programming principles by allowing counter variables to be used outside of the scope of the loop block
if they are defined outside the loop. Avoid the looseness of the language by always localizing the loop variable.

The enhanced for statement allows iteration over a full set of items or objects. For example:

import java.io.*;
import java.util.*;

public class task {

private static boolean uspeh = true;

public static void main(String args[]){

System.out.println( "Enter value for n : " );
int n = procitajBroj();

int zbir = 0;

while( n > 0 ){
zbir = zbir + n*n;
n--;
}

System.out.println("Result : " + zbir);

}

public static int procitajBroj() {
int result = 0;

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st;

do {
try {
st = new StringTokenizer(br.readLine());
result = Integer.parseInt(st.nextToken());

if(result > 0)
uspeh = true;
else
throw new Exception();

}
catch(Exception nfe) {
System.out.print("Error in input. Enter again: ");
uspeh = false;
}

}
while(!uspeh);

return result;
}
}

class GroupOfFunctions1 { public GroupOfFunctions1(){} //default constructor public int aFunc(int n) { return n * 2; } } class GroupOfFunctions2 { public GroupOfFunctions2(){} //default constructor //note the 'static' keyword: public static int anotherFunc(int n) { return n * 10; } } public class DemoFunctions { //main() is 'static', so java can kick off execution of //your program without creating on object of this class: public static void main(String[] args) { GroupOfFunctions1 obj1 = new GroupOfFunctions1(); int resultA = obj1.aFunc(10); int resultB = GroupOfFunctions2.anotherFunc(10); System.out.println(resultA); System.out.println(resultB); } }

Microsoft would prefer its own version of Java and libraries to be the standard. 10,000 developers who want Java's to be a cross-platform language have formed the Java Lobby.

Sun sued MicroSoft for abusing its licence of Java by giving out a version that will work with only MicroSoft software rather than on all platforms. So far(Winter 1998-1999) Microsoft has been ordered to stop giving out their polluted version and have been forced to distribute an upgrade to the "Pure Java" version.

Type	Description	Size
int	The integer type, with range -2,147,483,648 . . . 2,147,483,647	4 bytes
byte	The type describing a single byte, with range -128 . . . 127	1 byte
short	The short integer type, with range -32768 . . . 32767	2 bytes
long	The long integer type, with range -9,223,372,036,854,775,808 . . . -9,223,372,036,854,775,807	8 bytes
double	The double-precision floating-point type, with a range of about Â±10³⁰⁸ and about 15 significant decimal digits	8 bytes
float	The single-precision floating-point type, with a range of about Â±10³⁸ and about 7 significant decimal digits	4 bytes
char	The character type, representing code units in the Unicode encoding scheme	2 bytes
boolean	The type with the two truth values false and true	1 bit

Conditional Statements

Loops