“实例”链组装一个物体

Question

我面临以下代码：

public class BaseGroup {

    private Group1 group1;
    private Group2 group2;
    private Group3 group3;

    public void setGroup (IGroup group) {

        if(group instanceof Group1) {
            setGroup1((Group1) group);
        } else if(group instanceof Group2) {
            setGroup2((Group2) group);
        } else {
            setGroup3((Group3) group);
        }
    }

    public Group1 getGroup1() {
        return group1;
    }

    public void setGroup1(Group1 group1) {
        this.group1 = group1;
    }

    public Group2 getGroup2() {
        return group2;
    }

    public void setGroup2(Group2 group1) {
        this.group2 = group2;
    }

    public Group3 getGroup3() {
        return group3;
    }

    public void setGroup3(Group3 group1) {
        this.group3 = group3;
    }

}   

BaseGroup 类就是以这种方式使用的。

BaseGroup baseGroup = New BaseGroup();
basegroup.setGroup(group);

我的问题是关于调用相应设置器来组装 BaseGroup 对象的“instanceof”链。执行此操作的更好方法是什么？

Answer 1

您可以添加一个方法

interface IGroup {
    public void addToGroup(BaseGroup bg);
}

class Group1 implements IGroup {
    public void addToGroup(BaseGroup bg) { bg.setGroup1(this); }
}
// etc for Group2 and 3.


IGroup group;
BaseGroup bg;
group.addToGroup(bg);

Answer 2

取决于您如何使用group1、'group2'、'group3'。类似的东西可以工作：

class BaseGroup {
    private final List<Group> groups = new ArrayList<Group>();

    public void addGroup(Group group) {
         groups.add(group);
    }
}

Answer 3

多态性（特别是方法重载）实际上可能在这里起作用。

public void setGroup(Group1 group) {
  this.group1 = group;
}
public void setGroup(Group2 group) {
  this.group2 = group;
}
public void setGroup(Group3 group) {
  this.group3 = group;
}

Java会自动选择合适的方法。

Answer 4

另一种选择是使用反射。

Answer 5

public class BaseGroup {

private Map<Class<IGroup>, IGroup> groupsFactoryByClass;

public void setGroup (IGroup group) {
    IGroup oldGroup = groupsFactoryByClass.put(group.getClass());
    if (oldGroup != null)
        throw new IllegalArgumentException("Group with class " + group.getClass().getName() + " already set");
}

public <T implements IGroup> getGroup(Class<T> klazz) {
    return groupsFactoryByClass.get(klazz);
}
}

Answer 6

interface Group{}
class Group1 implements Group{}
class Group2 implements Group{}
class Group3 implements Group{}


public class BaseGroup {

    private Map<Class<Group>, <Group>>  groups = new HashMap<Class<Group>, <Group>>();

    public void setGroup (Group group) {
        groups.put(group.getClass(), group);
    }

}

Answer 7

最好避免的情况是访问者模式，请使用该模式。