例子: class Soup { private Soup() {} // (1) Allow creation via static method: public static Soup makeSoup() { return new Soup(); } // (2) Create a static object and // return a reference upon request. // (The "Singleton" pattern): private static Soup ps1 = new Soup(); public static Soup access() { return ps1; } public void f() {} }class Sandwich { // Uses Lunch void f() { new Lunch(); } }// Only one public class allowed per file: public class Lunch { void test() { // Can't do this! Private constructor: //! Soup priv1 = new Soup(); Soup priv2 = Soup.makeSoup(); Sandwich f1 = new Sandwich(); Soup.access().f(); } }
④:实际上,Java 1.1内部类既可以是“受到保护的”,也可以是“私有的”,但那属于特别情况。第7章会详细解释这个问题。⑤:亦可通过从那个类继承来实现。
class Soup {
private Soup() {}
// (1) Allow creation via static method:
public static Soup makeSoup() {
return new Soup();
}
// (2) Create a static object and
// return a reference upon request.
// (The "Singleton" pattern):
private static Soup ps1 = new Soup();
public static Soup access() {
return ps1;
}
public void f() {}
}class Sandwich { // Uses Lunch
void f() { new Lunch(); }
}// Only one public class allowed per file:
public class Lunch {
void test() {
// Can't do this! Private constructor:
//! Soup priv1 = new Soup();
Soup priv2 = Soup.makeSoup();
Sandwich f1 = new Sandwich();
Soup.access().f();
}
}