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);

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 i = (int) c;
        System.out.println(i);
        }

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)   {   }