static String valueOf(boolean b) 
or 
static String valueOf(char c) 
or
static String valueOf(char[] data) 
or
static String valueOf(char[] data, int offset, int count) 
or
static String valueOf(double d) 
or
static String valueOf(float f) 
or
static String valueOf(int i)
or
static String valueOf(long l)
or
static String valueOf(Object obj)

import java.io.*;
public class Test {

   public static void main(String args[]) {
      double d = 102939939.939;
      boolean b = true;
      long l = 1232874;
      char[] arr = {'a', 'b', 'c', 'd', 'e', 'f','g' };

      System.out.println("Return Value : " + String.valueOf(d) );
      System.out.println("Return Value : " + String.valueOf(b) );
      System.out.println("Return Value : " + String.valueOf(l) );
      System.out.println("Return Value : " + String.valueOf(arr) );
   }
}

Return Value : 1.02939939939E8
Return Value : true
Return Value : 1232874
Return Value : abcdefg