A private constructor is a special instance constructor. It is generally used in classes that contain static members only. If a class has one or more private constructors and no public constructors, other classes (except nested classes) cannot create…

Principle When implement the singleton pattern please decorate the INSTANCE field with "static final" and decorate the constructor with "private". // Singleton with static factory public class Elvis { private static final Elvis INSTANC…

A class can be made noninstantiable by including a private constructor. // Noninstantiable utility class public class UtilityClass { // Suppress default constructor for noninstantiability private UtilityClass() { throw new AssertionError(); } ... //…

Item4:Enforce noninstantiability with a private constructor 通过构造私有化,禁止对象被实例化. public class UtilClass { private UtilClass(){ //防止类内的函数调用构造函数创建对象 throw new AssertionError(); } }…

Item3:Enforce the singleton property with a private constructor or an enum type 采用枚举类型(ENUM)实现单例模式. public enum Elvis { INSTANCE; public void leaveTheBuiding(){ System.out.println("a single-element enum type is the best way to implement a singleton&q…

如果你定义的类仅仅是包含了一些静态的方法和静态的字段,这些类一般是一些工具类,这些一般是设计为不能被实例化的. 1. Attempting to enforce noninstantiability by making a class abstract does not work. 2. a class can be made noninstantiable by including a private constructor // Noninstantiable utility class p…

sonarlint提示add a private constructor to hide the implicit public one Utility classes should not have public constructors Utility classes, which are collections of static members, are not meant to be instantiated. Even abstract utility classes, which…

14.1 In terms of inheritance, what is the effect of keeping a constructor private? 这道题问我们用继承特性时,如果建立一个私有的构建函数会怎样. 只有能访问该函数的私有变量或函数的东西才能访问私有构建函数,比如内部类就可以访问,比如类A是类Q的一个内部类,那么Q的其他内部类可以访问类A的私有构建函数. 由于一个子类可以调用父类的构建函数,类A可以被继承,所以只有类A的子类或者是类Q的其他子类可以访问类A的私有构建函…

 1. 通过一个公开的字段来获取单例 // Singleton with public final field public class Elvis { public static final Elvis INSTANCE = new Elvis(); private Elvis() { ... } public void leaveTheBuilding() { ... } } The main advantage of the public field approach is that th…

a problem where OO seems more natural to me, implementing a utility class not instantiable. how to prevent instantiation, thanks to http://stackoverflow.com/questions/10558393/prevent-instantiation-of-an-object-outside-its-factory-method/10558404#105…