Question

如果我在java中编写私有构造函数而不是像默认构造函数那样工作？私有构造函数在类中有什么用？

public class BillPughSingleton {
private BillPughSingleton() {
}

private static class LazyHolder {
    private static final BillPughSingleton INSTANCE = new BillPughSingleton();
}

public static BillPughSingleton getInstance() {
    return LazyHolder.INSTANCE;
}

}

还解释了此代码的工作原理以及返回的值

Answer 1

不带参数的私有构造函数阻止在BillPughSingleton范围之外创建 BillPughSingleton，例如

   // Compile time error: BillPughSingleton() is private 
   BillPughSingleton instance = new BillPughSingleton();

   // The right and the ONLY way to get (single) instance:
   BillPughSingleton instance = BillPughSingleton.getInstance();

如果没有构造函数（包括private BillPughSingleton()）被声明，

   // if no constructors are declared, this wrong call becomes possible
   BillPughSingleton instance = new BillPughSingleton();

可通过默认构造函数语法实现。

私有构造函数是默认构造函数，它的用途是什么？

1 个答案: