我正在用这样的类编写 API:

public class NKMPMission {
    private String name;
    private int age;
    public NKMPMission(String name, int age)
    {
         this.name  = name;
         this.age   = age;
    }
    public String getName() 
    {
       return name;
    }

    public int getAge() 
    {
       return age;
     }
   }

我的问题:

1. 如何确保此 NKMPMission 类的用户仅访问 getter？
2. 如何为这个功能引入setter，让我作为开发者可以设置，而用户不能设置？

最佳答案

通常的做法是完全不公开类，只公开该类的接口(interface)。一种面向公众的界面，一种面向开发人员的界面。

然后您需要一个工厂来创建它们。

/**
 * Expose this interface to the public.
 */
public interface INKMPMission {

    public String getName();

    public int getAge();

}

/**
 * Only expose this interface to developers.
 */
interface IDeveloperNKMPMission {

    public void setName(String name);

    public void setAge(int age);

}

public static class NKMPMissionFactory {

    /**
     * Expose only the INKMPMission construction.
     */
    public INKMPMission make(String name, int age) {
        return new NKMPMission(name, age);
    }

    /**
     * Protected version for developers.
     */
    IDeveloperNKMPMission forDeveloper(INKMPMission it) {
        return IDeveloperNKMPMission.class.cast(it);
    }

    /**
     * Private so no-one outside the factory knows about the inner workings.
     */
    private static class NKMPMission implements INKMPMission, IDeveloperNKMPMission {

        private String name;
        private int age;

        private NKMPMission(String name, int age) {
            this.name = name;
            this.age = age;
        }

        @Override
        public String getName() {
            return name;
        }

        @Override
        public int getAge() {
            return age;
        }

        @Override
        public void setName(String name) {
            this.name = name;
        }

        @Override
        public void setAge(int age) {
            this.age = age;
        }
    }
}

对于真正的偏执狂，您甚至可以使用代理。这将使通过反射使用 setter 变得困难(但并非不可能)。

    /**
     * Expose only the INKMPMission construction.
     */
    public INKMPMission make(String name, int age) {
        return new NKMPMissionProxy(new NKMPMission(name, age));
    }

    /**
     * Protected version for developers.
     */
    protected IDeveloperNKMPMission forDeveloper(INKMPMission it) {
        if (it instanceof NKMPMissionProxy) {
            it = ((NKMPMissionProxy) it).theMission;
        }
        return IDeveloperNKMPMission.class.cast(it);
    }

    /**
     * A proxy for the truly paranoid - makes using reflection more difficult (but not impossible)
     */
    private static class NKMPMissionProxy implements INKMPMission {
        private final NKMPMission theMission;

        private NKMPMissionProxy(NKMPMission theMission) {
            this.theMission = theMission;
        }

        @Override
        public String getName() {
            return theMission.getName();
        }

        @Override
        public int getAge() {
            return theMission.getAge();
        }


    }

关于java - 仅向客户端共享 getter 方法的最佳方法是什么？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33953327/