协同过滤算法java实现

协同过滤算法是一种常见的推荐算法，其中最流行的是基于用户的协同过滤和基于物品的协同过滤。以下是一个简单的基于用户的协同过滤算法的Java实现：

import java.util.*;

public class UserBasedCF {
    // 用户数
    private int userNum;
    // 物品数
    private int itemNum;
    // 用户评分矩阵
    private int[][] userItemMatrix;
    // 相似度矩阵
    private double[][] similarityMatrix;
    
    // 构造函数
    public UserBasedCF(int userNum, int itemNum, int[][] userItemMatrix) {
        this.userNum = userNum;
        this.itemNum = itemNum;
        this.userItemMatrix = userItemMatrix;
        similarityMatrix = new double[userNum][userNum];
    }
    
    // 计算用户相似度
    public void computeSimilarity() {
        for (int i = 0; i < userNum; i++) {
            for (int j = i + 1; j < userNum; j++) {
                double similarity = computeUserSimilarity(i, j);
                similarityMatrix[i][j] = similarity;
                similarityMatrix[j][i] = similarity;
            }
        }
    }
    
    // 计算用户之间的相似度
    private double computeUserSimilarity(int user1, int user2) {
        int commonNum = 0;
        int sum1 = 0, sum2 = 0;
        int sumSq1 = 0, sumSq2 = 0;
        for (int i = 0; i < itemNum; i++) {
            if (userItemMatrix[user1][i] > 0 && userItemMatrix[user2][i] > 0) {
                commonNum++;
                int rating1 = userItemMatrix[user1][i];
                int rating2 = userItemMatrix[user2][i];
                sum1 += rating1;
                sum2 += rating2;
                sumSq1 += rating1 * rating1;
                sumSq2 += rating2 * rating2;
            }
        }
        if (commonNum == 0) {
            return 0;
        }
        double numerator = commonNum * (sum1 * sum2) - (sum1 * sum2);
        double denominator = Math.sqrt((commonNum * sumSq1 - sum1 * sum1) * (commonNum * sumSq2 - sum2 * sum2));
        if (denominator == 0) {
            return 0;
        }
        return numerator / denominator;
    }
    
    // 预测用户对物品的评分
    public double predictRating(int user, int item) {
        double numerator = 0;
        double denominator = 0;
        for (int i = 0; i < userNum; i++) {
            if (i != user && userItemMatrix[i][item] > 0) {
                double similarity = similarityMatrix[user][i];
                numerator += similarity * userItemMatrix[i][item];
                denominator += similarity;
            }
        }
        if (denominator == 0) {
            return 0;
        }
        return numerator / denominator;
    }
}

以上是一个简单的基于用户的协同过滤算法的Java实现。您可以根据您的需求进行修改和扩展。