Something like

String name = String.format("%s_%s%s_%s",n1,n2,n3,n4);

Using the String.format function

Using the String.format style (similar to C's 'printf' syntax) allows you to see the structure of your final string more clearly even when variable names are long. Overall it makes code easier to read then using the + operator, because you're separating your formatting text from the list of values you want in that format.

If you want to put the result in a String you can use :

String result = String.format("%-30s %-30s %-30s", divName, heading1, heading2);

Then you can print it or use it in another places

You can use String.format:

System.out.println(String.format("%s %s", First, Last));

Alternatively, you can just add a space there manually:

System.out.println(First + ' ' + Last);

From the docs:

• The format specifiers for general, character, and numeric types have the following syntax:

  %[argument_index$][flags][width][.precision]conversion     
  

The optional argument_index is a decimal integer indicating the position of the argument in the argument list. The first argument is referenced by "1$", the second by "2$", etc.

String.format("%1s %1s %1s", hello);