Calculate Swap The Two Numbers Using Java

import java.io.*; 
import java.text.*; 

class ssva20 
{ 
public static void main(String arg[]) throws IOException 
{ 
BufferedReader obj=new BufferedReader(new InputStreamReader(System.in)); 
System.out.println("\n SWAP TWO NUMBERS"); 
System.out.println(" ---- --- -------"); 
System.out.println("\n\tI N P U T"); 
System.out.println("\t- - - - -"); 
System.out.print("\n ENTER THE FIRST NUMBER (M) : "); 
double m=Double.parseDouble(obj.readLine()); 
System.out.print("\nENTER THE SECOND NUMBER (N) : "); 
double n=Double.parseDouble(obj.readLine()); 
NumberFormat nf=NumberFormat.getInstance(); 
nf.setMinimumFractionDigits(2); 
m=m+n; 
n=m-n; 
m=m-n; 
System.out.println("\n\tO U T P U T"); 
System.out.println("\t- - - - - -"); 
System.out.println("\n THE SWAP OF FIRST NUMBER (M) IS : "+nf.format(m)); 
System.out.println("\nTHE SWAP OF SECOND NUMBER (N) IS : "+nf.format(n)); 
System.out.println("\n\n"); 
} 
}