Java构造函数和静态方法 [英] Java Constructor and static method

问题描述

我何时应该使用构造函数，何时应该使用静态方法？

When should I use a constructor and when should I use static method?

您能用上面的小片段解释一下吗？我浏览了几个线程，但我仍然不清楚这一点。

Can you explain above with small snippet? I skimmed through a few threads but I'm still not clear with this.

推荐答案

当你只想要时使用公共构造函数返回一个类型的新对象，你想要简单。

Use a public constructor when you only ever want to return a new object that type and you want simplicity.

一个很好的例子是StringBuilder，因为它是可变的，你可能每次都想要一个新对象。

A good example is StringBuilder as it's mutable and you are likely to want a new object each time.

public String toString() {
    StringBuilder sb = new StringBuilder();
    // append fields to the sb
    return sb.toString();
}

当您可能想要重复使用对象时使用静态因子方法（尤其是如果是不可变的），你可能想要返回一个子类，或者你想要describeice构造。一个很好的例子是EnumSet，它有许多静态工厂，即使有些工具具有相同的参数，也会做不同的事情。

Use a static factor method when you might want to re-use objects (esp if immutable), you might want to return a sub-class or you want descriptice construction. A good example is EnumSet which has a number of static factories which do different things even though some have the same arguments.

EnumSet.noneOf(RetentionPolicy.class);
// has the same arguments, but is not the same as
EnumSet.allOf(RetentionPolicy.class);

在这种情况下，使用静态工厂可以清楚说明这两种构造方式之间的区别设置。

In this case, using a static factory makes it clear what the difference between these two ways of construction the set.

此外，EnumSet可以返回两个不同的实现，一个针对具有少量值的枚举进行优化（< = 64） RegularEnumSet 和另一个叫做 JumboEnumSet

Also EnumSet can return two different implementations, one optimised for enums with a small number of values (<= 64) RegularEnumSet and another for many values called JumboEnumSet

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