5: Controlling Program Flow with Decision-Making Statements in Java

Generating Code39 in Java 5: Controlling Program Flow with Decision-Making Statements

string To ask the second question (the more appropriate question) Java s String type has a method named equals (Like everything else in the known universe, this equals method is defined in the Java API, short for Application Programming Interface) The equals method compares two strings to see whether they have the same characters in them For an example using Java s equals method, see Listing 5-3 (A run of the program in Listing 5-3 is shown in Figure 5-4)

Listing 5-3:

import static javalangSystem*; import javautilScanner; class CheckPassword { public static void main(String args[]) { outprint( What s the password ); Scanner myScanner = new Scanner(in); String password = myScannernext(); outprintln( You typed >> + password + << ); outprintln(); if (password == swordfish ) { outprintln( The word you typed is stored ); outprintln( in the same place as the real ); outprintln( password You must be a ); outprintln( hacker ); } else { outprintln( The word you typed is not ); outprintln( stored in the same place as ); outprintln( the real password, but that s ); outprintln( no big deal ); } outprintln(); if (passwordequals( swordfish )) { outprintln( The word you typed has the ); outprintln( same characters as the real ); outprintln( password You can use our ); outprintln( precious system ); } else { outprintln( The word you typed doesn t ); outprintln( have the same characters as ); outprintln( the real password You can t ); outprintln( use our precious system ); } } }

In Listing 5-3, the call myScannernext() grabs whatever word the user types on the computer keyboard The code shoves this word into the variable named password Then the program s if statements use two different techniques to compare password with swordfish The more appropriate of the two techniques uses Java s equals method The equals method looks funny because when you call it you put a dot after one string and put the other string in parentheses But that s the way you have to do it In calling Java s equals method, it doesn t matter which string gets the dot and which gets the parentheses For instance, in Listing 5-3, you could have written if ( swordfish equals(password)) The method would work just as well A call to Java s equals method looks imbalanced, but it s not There s a reason behind the apparent imbalance between the dot and the parentheses The idea is that you have two objects: the password object and the swordfish object Each of these two objects is of type String (However, password is a variable of type String, and swordfish is a String literal) When you write passwordequals( swordfish ), you re calling an equals method that belongs to the password object As you call that method, you re feeding swordfish to the method as the method s parameter (pun intended) You can read more about methods belonging to objects in 7 When comparing strings with one another, use the equals method not the double equal sign

The first line of Listing 5-3 illustrates a lazy way of importing both System out and Systemin To import everything that System has to offer, you use the asterisk wildcard character (*) In fact, importing javalangSystem* is like having about 30 separate import declarations, including Systemin, Systemout, Systemerr, SystemnanoTime, and many other System things The use of an asterisk in an import declaration is generally considered bad programming practice, so I don t do it often in this book s examples But for larger programs programs that use dozens of names from the Java API the lazy asterisk trick is handy You can t toss an asterisk anywhere you want inside an import declaration For example, you can t import everything starting with java by writing import java* You can substitute an asterisk only for the name of a class or for the name of something static that s tucked away inside a class For more information about asterisks in import declarations, see 9 For information about static things, see 10