用户管理操作

用户信息包括【用户编号、用户名称、工资值和年龄】

随机生成若干个（>10）用户信息写入到一个二进制文件中，不允许id值重复，id也是随机生成的

长整型数值,在控制台上显示所有用户信息,删除第3个用户,将用户按照用户工资值从小到大排序后写回原文件

User类

import java.io.Serializable;

public class User implements Serializable, Comparable<User> {
	private static final long serialVersionUID = 3492921525397060568L;
	private Long id;// 用户编号
	private String username;// 用户名称
	private Double salary; // 工资
	private Integer age; // 年龄

	@Override
	/*
	  Math.abs(bb)：return (a <= 0.0D) ? 0.0D - a : a;
	  Math.abs(x)<1e-6其实相当于x == 0
    1e-6(也就是0.000001)叫做epslon，用来抵消浮点运算中因为误差造成的相等无法判断的情况。
                它通常是一个非常小的数字（具体多小要看你的运算误差）
	*/
	public int compareTo(User o) {
		double bb = this.salary - o.getSalary();
		if (Math.abs(bb) > 1e-6) {//
			if (bb > 0)
				return 1;
			else
				return -1;
		}
		return 0;
	}

	public Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	public String getUsername() {
		return username;
	}

	public void setUsername(String username) {
		this.username = username;
	}

	public Double getSalary() {
		return salary;
	}

	public void setSalary(Double salary) {
		this.salary = salary;
	}

	public Integer getAge() {
		return age;
	}

	public void setAge(Integer age) {
		this.age = age;
	}

	@Override
	public String toString() {
		return "User [id=" + id + ", username=" + username + ", salary=" + salary + ", age=" + age + "]";
	}

}

UserManger类

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Random;

public class UserManager {
	private static File file = new File("data/users.data");
	static {
		File ff = new File("data/");
		if (!ff.exists())
			ff.mkdirs();
		ObjectOutputStream oos = null;
		try {
			if (!file.exists()) {
				oos = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(file)));
				Random r = new Random();
				int num = r.nextInt(91) + 10;
				long[] idArr = new long[num];
				for (int i = 0; i < num; i++) {
					User tmp = new User();
					long kk = generateId(idArr);
					tmp.setId(kk);
					idArr[i] = kk;
					tmp.setUsername("name" + i);
					tmp.setSalary(r.nextDouble() * 10000);
					tmp.setAge(r.nextInt(10) + 10);
					oos.writeObject(tmp);
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if (oos != null)
					oos.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}

	public void sort() throws IOException, ClassNotFoundException {
		Object[] res = null;
		ArrayList list = getAllUsers();
		int len = 0;
		if (list != null) {
			res = list.getData();
			// 这个方法不唯一
			for (int i = 0; i < res.length; i++) {
				if (res[i] != null) {
					len++;
					continue;
				} else
					break;
			}
			for (int i = 1; i < len; i++) {
				for (int k = 0; k < len - i; k++) {
					if (res[k] != null && res[k] instanceof User) {
						User tmp1 = (User) res[k];
						if (res[k + 1] != null && res[k + 1] instanceof User) {
							User tmp2 = (User) res[k + 1];
							if (tmp1.compareTo(tmp2) > 0) {
								Object tmp = res[k];
								res[k] = res[k + 1];
								res[k + 1] = tmp;
							}
						}
					}
				}
			}
		}
		try (ObjectOutputStream oos = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(file)));) {
			if (res != null && res.length > 0) {
				for (Object tmp : res) {
					if(tmp!=null) {
						oos.writeObject(tmp);
					}
				}
			}
		}
	}

	public ArrayList getAllUsers() throws IOException, ClassNotFoundException {
		ArrayList res = new ArrayList();
		if (file.exists()) {
			try (ObjectInputStream ois = new ObjectInputStream(new BufferedInputStream(new FileInputStream(file)))) {
				while (true) {
					try {
						Object obj = ois.readObject();
						res.add(obj);
					} catch (EOFException e) {
						break;
					}
				}
			}
		}
		return res;
	}

	public void remove(int index) throws IOException, ClassNotFoundException {
		ArrayList list = this.getAllUsers();
		list.remove(index);
		try (ObjectOutputStream oos = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(file)));) {
			Object[] array = list.getData();
			for (Object tmp : array) {
				if (tmp != null)
					oos.writeObject(tmp);
			}
		}
	}

	private static long generateId(long[] idArr) {
		long res = 0L;
		Random r = new Random();
		while (true) {
			// id>0
			long kk = r.nextLong();
			if (kk > 0) {
				boolean exists = false;
				for (int k = 0; k < idArr.length; k++) {
					if (idArr[k] == kk) {
						exists = true;
						break;
					}
				}
				if (!exists) {
					res = kk;
					break;
				}
			}
		}
		return res;
	}

	public static void main(String[] args) throws Exception {
		UserManager um = new UserManager();
		for (Object tmp : um.getAllUsers().getData())
			System.out.println(tmp);

	}
}

Arraylist类

public class ArrayList {
	private Object[] array;
	private static final int CAPACITY = 10;

	public ArrayList() {
		this(CAPACITY);
	}

	public ArrayList(int capacity) {
		array = new Object[capacity];
	}

	public void remove(int index) {
		if (index > array.length)
			throw new ArrayIndexOutOfBoundsException();
		Object end = array[array.length - 1];
		System.arraycopy(array, index, array, index - 1, array.length - index);
		if (end != null) {
			array[array.length - 1] = null;
		}
	}

	public void add(Object obj) {
		if (obj != null) {
			boolean flag = false;
			for (int i = 0; i < array.length; i++) {
				if (array[i] == null) {
					array[i] = obj;
					flag = true;
					break;
				}
			}
			int len = array.length;
			if (!flag) {
				int newLen = len * 2;
				Object[] newArr = new Object[newLen];
				System.arraycopy(array, 0, newArr, 0, array.length);
				this.array = newArr;
				array[len] = obj;
			}
		}
	}

	public Object[] getData() {
		return this.array;
	}
}