帮我用java语言解决基于优先队列式分支限界法解决0-1背包问题，给出实例具体展示，给出具体实现代码

好的，以下是基于优先队列式分支限界法解决0-1背包问题的Java代码实现：

import java.util.Comparator;
import java.util.PriorityQueue;

public class KnapsackProblem {

    static class Node {
        int level;
        int profit;
        int weight;
        double bound;

        public Node(int level, int profit, int weight, double bound) {
            this.level = level;
            this.profit = profit;
            this.weight = weight;
            this.bound = bound;
        }
    }

    static class NodeComparator implements Comparator<Node> {
        @Override
        public int compare(Node n1, Node n2) {
            return Double.compare(n2.bound, n1.bound);
        }
    }

    public static int knapsack(int[] weights, int[] profits, int capacity) {
        int n = weights.length;
        PriorityQueue<Node> pq = new PriorityQueue<>(new NodeComparator());
        pq.offer(new Node(-1, 0, 0, 0));

        int maxProfit = 0;
        while (!pq.isEmpty()) {
            Node node = pq.poll();

            if (node.level == n - 1) {
                continue;
            }

            int level = node.level + 1;
            int profit = node.profit + profits[level];
            int weight = node.weight + weights[level];

            if (weight <= capacity && profit > maxProfit) {
                maxProfit = profit;
            }

            double bound = calculateBound(profits, weights, capacity, level, profit, weight);
            if (bound > maxProfit && weight <= capacity) {
                pq.offer(new Node(level, profit, weight, bound));
            }

            pq.offer(new Node(level, node.profit, node.weight, bound));
        }

        return maxProfit;
    }

    private static double calculateBound(int[] profits, int[] weights, int capacity, int level, int profit, int weight) {
        double bound = profit;
        int n = weights.length;

        while (level < n && weight < capacity) {
            bound += profits[level] * (capacity - weight) / (double) weights[level];
            weight += weights[level];
            level++;
        }

        return bound;
    }

    public static void main(String[] args) {
        int[] weights = {10, 20, 30};
        int[] profits = {60, 100, 120};
        int capacity = 50;

        int maxProfit = knapsack(weights, profits, capacity);
        System.out.println("Max profit: " + maxProfit);
    }
}

以上代码实现了基于优先队列式分支限界法解决0-1背包问题，其中 `calculateBound` 方法用于计算节点的上界。在 `main` 方法中，我们使用了一个示例，输入了一组数据，输出了最大收益。