[理学]Java面向对象编程23.ppt

Notice that the static members of the class are underlined. In this pattern: The static attribute instance contains the single instance of the class. The constructor is defined as private so that other classes cannot create instances. The static method getSingletonInstance returns the single instance of the class. The first time this method is called, it creates the single instance. public class ICarnegieInfo ? { ??? static private ICarnegieInfo singletonInstance = null; ??? private String name; ??? private String address; ??? private String telephone; ??? private ICarnegieInfo () { ??????? name = iCarnegie, Inc; ??????? address = 4615 Forbes Avenue Pittsburgh, PA 15213-3796; ??????? telephone = 1.412.622.2150; ??? } ??? static public ICarnegieInfo getSingletonInstance() { ??????? if (singletonInstance == null) { ??????????? singletonInstance = new ICarnegieInfo(); ??????? } ??????? return singletonInstance; ??? } ??? public String getName() { ??????? return name; ??? } ??? public String getAddress() { ??????? return address; ??? } ??? public String getTelephone() { ??????? return telephone; ??? } }  import ? java.io.*; public class ICarnegieInfoDemo ? { ??? private static PrintWriter ? stdOut = ??????? new ? PrintWriter(System.out, true); ??? public static void main(String[] ? args) ? { ??????? ICarnegieInfo companyInfo = ??????????? ICarnegieInfo.getSingletonInstance(); ??????? stdOut.println(Name: + companyInfo.getName()); ??????? stdOut.println(Address: + companyInfo.getAddress()); ??????? stdOut.println(Telephone: + companyInfo.getTelephone()); ??? } } Consequences The singleton pattern has the following benefits: A singleton class can control how and when client code accesses the single instance. Client code does not have the freedom to use the new operator to create an instance of the singleton class. Instead, it must call a static method that returns a reference to the single instance. A singleton c