Question

我需要一个简单的数据库，比如索引搜索的结构。它将在applet中使用，因此我不想使用额外的嵌入式数据库jar。

总结：我试着用一个神学来解释。例如学生表：

Students
------------------
Score
Gender
Name

我想过滤SCORE > 40 AND SCORE < 80 AND GENDER = MALE 我找到的解决方案进行全表扫描。但我正在寻找像TreeMap这样的解决方案。

我做了一个简单的解决方案，比如使用TreeMap进行分区。

package multikey;

import java.util.ArrayList;
import java.util.List;
import java.util.SortedMap;
import java.util.TreeMap;


public class MultiKey {




    public MultiKey() {

        final Integer MALE   = 1;
        final Integer FEMALE = 2;

        List<Student>                                    students = new ArrayList<Student>();
        TreeMap<Integer, TreeMap<Integer, List<String>>> table;

        students.add(new Student(80, MALE, "John"));
        students.add(new Student(80, FEMALE, "Monica"));
        students.add(new Student(70, MALE, "Michael"));
        students.add(new Student(60, MALE, "Brad"));
        students.add(new Student(60, FEMALE, "Angelina"));
        students.add(new Student(50, MALE, "Steve"));
        students.add(new Student(40, MALE, "Alex"));

        table = new TreeMap<Integer, TreeMap<Integer, List<String>>>();

        for (Student student : students) {
            Integer                        score     = student.score;
            Integer                        gender    = student.gender;
            TreeMap<Integer, List<String>> genderMap;
            List<String>                   names;

            if ((genderMap = table.get(score)) == null) {
                genderMap = new TreeMap<Integer, List<String>>();
                table.put(score, genderMap);
            }

            if ((names = genderMap.get(gender)) == null) {
                names = new ArrayList<String>();
                genderMap.put(gender, names);
            }

            names.add(student.name);
        }

        // 50 - 70 arasında alan erkekler
        SortedMap<Integer, TreeMap<Integer, List<String>>> students5070 = table.subMap(50, 71);
        List<String>                                       filtered     = new ArrayList<String>();

        for (Integer score : students5070.keySet()) {
            filtered.addAll(students5070.get(score).get(MALE));
        }

        System.out.println(filtered);
    }



    public static void main(String[] args) {

        new MultiKey();
    }




    public class Student {




        private int    gender;
        private String name;
        private int    score;




        public Student(int score, int gender, String name) {

            this.score  = score;
            this.gender = gender;
            this.name   = name;
        }




        public int getGender() {

            return gender;
        }



        public String getName() {

            return name;
        }




        public int getScore() {

            return score;
        }




        @Override
        public String toString() {

            return name;
        }
    }
}

Answer 1

如果您只需要一张桌子，guava tables可能会对您有所帮助，仅作为参考。如果你需要更多类似SQL的语法...我认为你不能避免使用类似纯粹的hava SQL数据库这样的东西，如HSQLDB

表格像索引集合过滤

1 个答案: