All programming languages have some form of an if
statement that tests conditions. In the previous code you should have tested whether there actually were command line arguments before you tried to use them.
Arrays have lengths and you can access that length by referencing the variable arrayname.length
You test the length of the args
array as follows.
// This is the Hello program in Java
class Hello {
public static void main (String args[]) {
if (args.length > 0) {
System.out.println("Hello " + args[0]);
}
}
}
System.out.println(args[0])
was wrapped in a conditional test, if (args.length > 0) { }
. The code inside the braces, System.out.println(args[0])
, now gets executed if and only if the length of the args array is greater than zero.
The arguments to a conditional statement like if
must be a boolean value,
that is something that evaluates to true or false. Integers are not
permissible.
In Java numerical greater than and lesser than tests are done with the >
and <
operators respectively. You can test whether a number is less than or equal to or greater than or equal to another number with the <=
and >=
operators.