Java多对多关联图

问题内容：

我有两堂课，ClassA和一堂课，ClassB“一对多”
AssociationClass。我想要一个结构，其中包含A和B之间的关联，以便我可以找到A或B的每个实例的对应对象。

我想到了使用带对键的Hashmap：

Hasmap<Pair<ClassA, ClassB>, AssociationClass> associations;

这样一来，我可以添加和删除的两个实例之间的关联ClassA和ClassB，我可以查询两个给定的情况下的关系。

但是，我错过了为ClassA或给定实例定义所有关联的功能ClassB。

我可以通过蛮力做到这一点，并在地图的所有键上循环以搜索给定实例之间的关联，但这效率低下而且不够优雅。

您是否知道任何启用此功能的数据结构/免费库？我不想重新发明轮子。

注意：这不是“数据库”问题。这些对象是用于实时计算的纯POJO，我不需要持久性东西。

问题答案：

感谢您的建议。

我终于重新发明了轮子……我编写了一个用于持有关联的通用类。我使用两张同步的地图。

协会持有人提供以下方法

void setAssociation(LeftClass left, RightClass right, AssociationClass assoc);
AssociationClass getAssociation(LeftClass left, RightClass right);
Map<RightClass, AssociationClass> getAssocationsLeft(LeftClass left);
Map<LeftClass, AssociationClass> getAssocationsRight(RightClass right); 
void removeAssociation(LeftClass left, RightClass right);

这是代码：

import java.util.HashMap;

/** This class holds many to many associations between two classes. */
public class AssociationHolder<LeftClass, RightClass, AssociationClass> {

    // -------------------------------------------------------
    // Attributes
    // -------------------------------------------------------

    private HashMap<LeftClass, HashMap<RightClass, AssociationClass>> associationsLeft = 
        new HashMap<LeftClass, HashMap<RightClass,AssociationClass>>();
    private HashMap<RightClass, HashMap<LeftClass, AssociationClass>> associationsRight = 
        new HashMap<RightClass, HashMap<LeftClass,AssociationClass>>();

    // -------------------------------------------------------
    // Methods
    // -------------------------------------------------------

    /** 
     *  Set an association between two instance.
     *  Any prior association is overwritten.
     */
    public void setAssociation(LeftClass left, RightClass right, AssociationClass association) {

        // Get the map for the left 
        HashMap<RightClass, AssociationClass> leftMap = this.associationsLeft.get(left);

        // No association defined yet for this left key ? => Create new map
        if (leftMap == null) {
            leftMap = new HashMap<RightClass, AssociationClass>();
            this.associationsLeft.put(left, leftMap);
        }

        // Get the map for the right 
        HashMap<LeftClass, AssociationClass> rightMap = this.associationsRight.get(right);

        // No association defined yet for this right key ? => Create new map
        if (rightMap == null) {
            rightMap = new HashMap<LeftClass, AssociationClass>();
            this.associationsRight.put(right, rightMap);
        }

        // Set the assoication on both maps
        leftMap.put(right, association);
        rightMap.put(left, association);

    }

    /** @return null if no association found. */
    public AssociationClass getAssociation(LeftClass left, RightClass right) {

        // Use left maps (could have used the right one as well)
        HashMap<RightClass, AssociationClass> leftMap = this.associationsLeft.get(left);
        if (leftMap == null) return null;
        return leftMap.get(right);
    }

    /** Get all associations defined for a given Left instance.  */
    public HashMap<RightClass, AssociationClass> getAssociationsLeft(LeftClass left) {

        HashMap<RightClass, AssociationClass> leftMap = this.associationsLeft.get(left);

        // No map defined ? return empty one instead of null
        if (leftMap == null) {
            return new HashMap<RightClass, AssociationClass>();
        } else {
            return leftMap;
        }   
    }

    /** Get all associations defined for a given Right instance.  */
    public HashMap<LeftClass, AssociationClass> getAssociationsRight(RightClass right) {

        HashMap<LeftClass, AssociationClass> rightMap = this.associationsRight.get(right);

        // No map defined ? return empty one instead of null
        if (rightMap == null) {
            return new HashMap<LeftClass, AssociationClass>();
        } else {
            return rightMap;
        }   
    }

    /** 
     *  Remove an association between two instances.
     */
    public void removeAssociation(LeftClass left, RightClass right) {
        HashMap<RightClass, AssociationClass> leftMap = this.getAssociationsLeft(left);
        HashMap<LeftClass, AssociationClass> rightMap = this.getAssociationsRight(right);
        leftMap.remove(right);      
        rightMap.remove(left);  
    }
}

我希望这可以在将来对某人有所帮助。

Java多对多关联图

微信关注