This example detects a mistake:
 

import java.io.*;

// javac wrong_casting.java
public class wrong_casting
{
public static void main(String args[])throws IOException
{
/*this is a comment
compile as
javac multi_comment.java
call as java simple_comment */
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

System.out.print("Type numbers only: ");
String str = "";
str = br.readLine();
System.out.println(str);
double d1 = Double.parseDouble(str);
System.out.println();
System.out.println(d1 += d1);
int n1 = (double)d1;
System.out.println("--data rounding--due to casting--");
System.out.println(n1);

}
}