如何在BST中插入学生数据对象？求策略模式实现参考资源

核心思路 #

策略模式的核心是把比较逻辑从BST中抽离，让BST可以动态切换不同的排序规则（比如按学号、GPA、姓名排序）来插入学生对象。这样BST的核心结构不用修改，只需要替换比较策略就能适配不同的插入需求。

步骤1：定义学生数据类 #

先封装学生的核心数据，提供必要的访问方法：

public class Student {
    private String firstName;
    private String lastName;
    private String studentId;
    private double gpa;

    public Student(String firstName, String lastName, String studentId, double gpa) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.studentId = studentId;
        this.gpa = gpa;
    }

    // Getter方法，供策略类访问字段
    public String getFirstName() { return firstName; }
    public String getLastName() { return lastName; }
    public String getStudentId() { return studentId; }
    public double getGpa() { return gpa; }
}

步骤2：定义比较策略接口 #

创建一个统一的策略接口，所有具体的比较规则都要实现这个接口：

public interface StudentComparisonStrategy {
    // 返回值规则：<0则a排在b前面，>0则b排在a前面，=0则相等
    int compare(Student a, Student b);
}

步骤3：实现具体的比较策略 #

根据不同的排序需求，实现对应的策略类：

• 按学号排序的策略：

public class StudentIdStrategy implements StudentComparisonStrategy {
    @Override
    public int compare(Student a, Student b) {
        return a.getStudentId().compareTo(b.getStudentId());
    }
}

• 按GPA降序排序的策略：

public class GpaDescStrategy implements StudentComparisonStrategy {
    @Override
    public int compare(Student a, Student b) {
        // 降序：b的GPA减a的GPA，返回值反转
        return Double.compare(b.getGpa(), a.getGpa());
    }
}

• 按姓氏+名字排序的策略：

public class FullNameStrategy implements StudentComparisonStrategy {
    @Override
    public int compare(Student a, Student b) {
        int lastNameCompare = a.getLastName().compareTo(b.getLastName());
        if (lastNameCompare != 0) {
            return lastNameCompare;
        }
        // 姓氏相同则比较名字
        return a.getFirstName().compareTo(b.getFirstName());
    }
}

步骤4：改造BST以支持策略模式 #

让BST持有一个比较策略实例，插入时使用该策略判断节点位置：

public class StudentBST {
    private class Node {
        Student data;
        Node left;
        Node right;

        Node(Student data) {
            this.data = data;
            left = right = null;
        }
    }

    private Node root;
    private StudentComparisonStrategy strategy;

    // 构造时传入指定的比较策略
    public StudentBST(StudentComparisonStrategy strategy) {
        this.root = null;
        this.strategy = strategy;
    }

    // 对外暴露的插入方法
    public void insert(Student student) {
        root = insertRecursive(root, student);
    }

    // 递归实现插入逻辑
    private Node insertRecursive(Node current, Student student) {
        if (current == null) {
            return new Node(student);
        }

        // 使用策略比较当前节点和待插入学生
        int comparison = strategy.compare(student, current.data);
        if (comparison < 0) {
            current.left = insertRecursive(current.left, student);
        } else if (comparison > 0) {
            current.right = insertRecursive(current.right, student);
        } else {
            // 相等时可选择忽略或更新，这里默认忽略重复
            return current;
        }
        return current;
    }
}

步骤5：使用示例 #

创建不同策略的BST并插入学生：

public class Main {
    public static void main(String[] args) {
        // 创建按学号排序的BST
        StudentBST idSortedBST = new StudentBST(new StudentIdStrategy());
        idSortedBST.insert(new Student("Alice", "Smith", "S1001", 3.8));
        idSortedBST.insert(new Student("Bob", "Jones", "S1003", 3.5));
        idSortedBST.insert(new Student("Charlie", "Brown", "S1002", 3.9));

        // 切换为按GPA降序的BST
        StudentBST gpaSortedBST = new StudentBST(new GpaDescStrategy());
        gpaSortedBST.insert(new Student("Alice", "Smith", "S1001", 3.8));
        gpaSortedBST.insert(new Student("Bob", "Jones", "S1003", 3.5));
        gpaSortedBST.insert(new Student("Charlie", "Brown", "S1002", 3.9));
    }
}

内容的提问来源于stack exchange，提问作者Pooja