Java集合框架实战项目教程

List<Student> students = new ArrayList<>();
students.add(new Student(1, "张三", 85));
students.add(new Student(2, "李四", 92));
students.add(new Student(3, "王五", 78));

// 遍历所有学生
for (Student s : students) {
    System.out.println(s);
}

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    Student student = (Student) o;
    return id == student.id;
}

@Override
public int hashCode() {
    return Integer.hashCode(id);
}

Map<Integer, Student> studentMap = new HashMap<>();
studentMap.put(1, new Student(1, "张三", 85));
studentMap.put(2, new Student(2, "李四", 92));

// 根据id查找
Student s = studentMap.get(1);
if (s != null) {
    System.out.println("找到学生：" + s);
} else {
    System.out.println("未找到该学生");
}

Map<String, Integer> gradeCount = new HashMap<>();
for (Student stu : students) {
    String level;
    if (stu.getScore() >= 90) level = "优秀";
    else if (stu.getScore() >= 80) level = "良好";
    else if (stu.getScore() >= 70) level = "中等";
    else if (stu.getScore() >= 60) level = "及格";
    else level = "不及格";

    gradeCount.put(level, gradeCount.getOrDefault(level, 0) + 1);
}
System.out.println("成绩分布：" + gradeCount);