Java中继承的最终常量值？

Question

我有以下问题.我想要一个名为MessageField的广泛抽象类型.MessageField的运行时使用是携带String值; 该类型的其余部分应该是一堆不变的定义和行为.MessageField的每个子类都应该是一组定义类型的常量最终成员,如果需要,还可以覆盖其他行为方法.

例如:

public abstract class MessageField {
   //whatever needs to go here to make this work
   //methods that define behavior
   //e.g. public int getFieldId() { return fieldId; }
}

public class TypeOne extends MessageField { 
    public final int fieldId = 1; //type defining member
    public final String tag = "->"; //type-defining member
    public String fieldValue; //freely settable/gettable
    //change any behavior if necessary
}

public class TypeTwo extends MessageField { 
    public final int fieldId = 2;
    public final String tag = "++";
    public String fieldValue;
}

public class TypeThree extends MessageField {
    public final int fieldId = 3;
    public final String tag = "blah";
    public String fieldValue;
}

应该强制每个子类在写入时为fieldId和tag定义一个值.我猜在概念上这些是每种类型的静态最终常量,但是它如何与继承一起工作？我需要所有各种类型以符合可以传递的一种广泛的总体类型.

也许继承不是实现这种模式的最佳方式,但如果没有,那是什么？如果继承是这样做的方式,它会怎么做？

谢谢!

Answer 1

将字段移动到基类并通过构造函数初始化它们:

public abstract class MessageField {
    public final int fieldId;
    public final String tag;

    protected MessageField(int fieldId, String tag) {
        this.fieldId = fieldId;
        this.tag = tag;
    }

    public int getFieldId() {
        return fieldId;
    }

    public String getTag() {
        return tag;
    }
}

public class TypeOne extends MessageField {
    public String fieldValue; //freely settable/gettable

    public TypeOne() {
        super(1, "->");
    }
}

// etc.

既然您考虑使用存取方法,我建议制作fieldId和tag private.