With the help of java, I have created concat() string method. In the example given below, I have used '+' operator , StringBuilder and StringBuffer Class to join string in java. The string concat() method combines specified string at the end of the primary string and returns combined string.

public class StringConcat{

    public static void main(String args[]) {

        String firstname = "Raj";
        String lastname = "Tiwari";

        //  concatenate String      
        String name = firstname + " " + lastname;
        System.out.println(name);


        //  using StringBuilder
        StringBuilder sb = new StringBuilder(14);
        sb.append(firstname).append(" ").append(lastname);
        System.out.println(sb.toString());


        //  using StringBuffer
        StringBuffer sBuffer = new StringBuffer(15);
        sBuffer.append(firstname).append(" ").append(lastname);
        System.out.println(sBuffer.toString());

    }     

}