用工厂方法替换构造函数

// File Class.java
public class Class {
    public Class(String s) {
        ...
    }
}

// File AnotherClass.java
public class AnotherClass {
    public void method() {
        Class aClass = new Class("string");
    }
}

// File Class.java
public class Class {
    private Class(String s) {
        ...
    }
    public static Class createClass(String s) {
        return new Class(s);
    }
}

// File AnotherClass.java
public class AnotherClass {
    public void method() {
        Class aClass = Class.createClass("string");
    }
}