Java之创建对象>4.Enforce noninstantiability with a private constructor

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
    public class UtilityClass {
    // Suppress default constructor for noninstantiability
    private UtilityClass() {
    throw new AssertionError();
    }
    ... // Remainder omitted
}