use stringbuilder

import java.util.*; 
import java.util.concurrent.LinkedBlockingQueue; 
  
public class GFG1 { 
    public static void main(String[] argv) throws Exception 
    { 
        StringBuilder str = new StringBuilder(); 
        str.append("GFG"); 
  
        StringBuilder str1 = new StringBuilder("AAAABBBCCCC"); 
  
        StringBuilder str2 = new StringBuilder(10); 
        StringBuilder str3 = new StringBuilder(str1); 
        System.out.println("String3 = " + str3.toString()); 
    } 
}