java1.定义一个学生类,包含 姓名 年龄,成绩三个属性, 添加20个学生信息 按照年龄排序 按照成绩排序 按照年龄和成绩排序 2.自定义数组的类 实现添加 删除 修改和获得长度的操作 3.获得30天后的时间 4,获得一年后的今天

1. 学生类的定义及排序实现

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public class Student {
    private String name;
    private int age;
    private int score;

    public Student(String name, int age, int score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public int getScore() {
        return score;
    }

    public static void main(String[] args) {
        ArrayList<Student> students = new ArrayList<>();
        students.add(new Student("Tom", 18, 90));
        students.add(new Student("Jane", 19, 80));
        students.add(new Student("Alice", 20, 70));
        // 添加20个学生信息 ...

        System.out.println("按照年龄排序：");
        Collections.sort(students, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                return s1.getAge() - s2.getAge();
            }
        });
        printStudents(students);

        System.out.println("按照成绩排序：");
        Collections.sort(students, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                return s2.getScore() - s1.getScore();
            }
        });
        printStudents(students);

        System.out.println("按照年龄和成绩排序：");
        Collections.sort(students, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                if (s1.getAge() == s2.getAge()) {
                    return s2.getScore() - s1.getScore();
                } else {
                    return s1.getAge() - s2.getAge();
                }
            }
        });
        printStudents(students);
    }

    public static void printStudents(ArrayList<Student> students) {
        for (Student s : students) {
            System.out.println(s.getName() + ", " + s.getAge() + ", " + s.getScore());
        }
        System.out.println();
    }
}

2. 自定义数组的类实现

public class MyArray {
    private int[] arr;
    private int size;

    public MyArray(int capacity) {
        arr = new int[capacity];
        size = 0;
    }

    public int getSize() {
        return size;
    }

    public int getCapacity() {
        return arr.length;
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public void add(int index, int element) {
        if (index < 0 || index > size) {
            throw new IllegalArgumentException("Add failed. Index is invalid.");
        }
        if (size == arr.length) {
            resize(2 * arr.length);
        }
        for (int i = size - 1; i >= index; i--) {
            arr[i + 1] = arr[i];
        }
        arr[index] = element;
        size++;
    }

    public void addLast(int element) {
        add(size, element);
    }

    public void addFirst(int element) {
        add(0, element);
    }

    public int get(int index) {
        if (index < 0 || index >= size) {
            throw new IllegalArgumentException("Get failed. Index is invalid.");
        }
        return arr[index];
    }

    public void set(int index, int element) {
        if (index < 0 || index >= size) {
            throw new IllegalArgumentException("Set failed. Index is invalid.");
        }
        arr[index] = element;
    }

    public boolean contains(int element) {
        for (int i = 0; i < size; i++) {
            if (arr[i] == element) {
                return true;
            }
        }
        return false;
    }

    public int find(int element) {
        for (int i = 0; i < size; i++) {
            if (arr[i] == element) {
                return i;
            }
        }
        return -1;
    }

    public int remove(int index) {
        if (index < 0 || index >= size) {
            throw new IllegalArgumentException("Remove failed. Index is invalid.");
        }
        int ret = arr[index];
        for (int i = index + 1; i < size; i++) {
            arr[i - 1] = arr[i];
        }
        size--;
        if (size == arr.length / 4 && arr.length / 2 != 0) {
            resize(arr.length / 2);
        }
        return ret;
    }

    public int removeFirst() {
        return remove(0);
    }

    public int removeLast() {
        return remove(size - 1);
    }

    public void removeElement(int element) {
        int index = find(element);
        if (index != -1) {
            remove(index);
        }
    }

    private void resize(int newCapacity) {
        int[] newArr = new int[newCapacity];
        for (int i = 0; i < size; i++) {
            newArr[i] = arr[i];
        }
        arr = newArr;
    }
}

3. 获得30天后的时间

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class GetDate {
    public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Calendar calendar = Calendar.getInstance();
        Date now = calendar.getTime();
        System.out.println("当前时间是：" + sdf.format(now));
        calendar.add(Calendar.DATE, 30);
        Date after30Days = calendar.getTime();
        System.out.println("30天后的时间是：" + sdf.format(after30Days));
    }
}

4. 获得一年后的今天

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class GetDate {
    public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Calendar calendar = Calendar.getInstance();
        Date now = calendar.getTime();
        System.out.println("当前时间是：" + sdf.format(now));
        calendar.add(Calendar.YEAR, 1);
        Date nextYear = calendar.getTime();
        System.out.println("一年后的今天是：" + sdf.format(nextYear));
    }
}