type casting

integer to String : 
 int i = 42;
 String str = Integer.toString(i); or String str = "" + i
 
double to String : 
 String str = Double.toString(i);
 
long to String : 
 String str = Long.toString(l);
 
float to String : 
 String str = Float.toString(f);

String to integer :
 str = "25";
 int i = Integer.valueOf(str).intValue(); or int i = Integer.parseInt(str);
 
String to double : 
 double d = Double.valueOf(str).doubleValue();
 
String to long : 
 long l = Long.valueOf(str).longValue(); or long l = Long.parseLong(str);
 
String to float : 
 float f = Float.valueOf(str).floatValue();

decimal to binary : 
 int i = 42; String binstr = Integer.toBinaryString(i);

decimal to hexadecimal : 
 int i = 42; String hexstr = Integer.toString(i, 16);
 or String hexstr = Integer.toHexString(i);
 or (with leading zeroes and uppercase)
 
 public class Hex { public static void main(String args[])
 {
  int i = 42;
  System.out.print(Integer.toHexString( 0x10000 | i).substring(1).toUpperCase());
  }
 } 

hexadecimal (String) to integer : 
 int i = Integer.valueOf("B8DA3", 16).intValue(); or int i = Integer.parseInt("B8DA3", 16); 

ASCII code to String 
 int i = 64;
 String aChar = new Character((char)i).toString();

integer to ASCII code (byte) 
 char c = 'A';
 int i = (int) c; // i will have the value 65 decimal

To extract Ascii codes from a String 
 String test = "ABCD";
 for ( int i = 0; i < test.length(); ++i )
 {
  char c = test.charAt( i );
  int j = (int) c;
  System.out.println(j);
 }

integer to boolean 
 b = (i != 0);
 
boolean to integer 
 i = (b)?1:0;
 
note :
 To catch illegal number conversion, try using the try/catch mechanism.
 
 try{
  i = Integer.parseInt(aString);
 }
 catch(NumberFormatException e)
 {
 }