第20 章 ： JavaIO编程案例

91 数字大小比较

输入3个整数，并求出3个整数最大值和最小值

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;


class InputUtil {
    /**
     * 读取指定个数的整数输入
     *
     * @param num 指定要输入的整数个数
     * @return 所有读取的整数数组
     * @throws IOException
     */
    public static int[] getIntList(int num) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        System.out.println("请输入" + num + "个整数：");

        int[] list = new int[num];
        int count = 0;

        while (count < num) {
            String msg = reader.readLine();

            if (msg.matches("\\d+")) {
                list[count++] = Integer.parseInt(msg);
            } else {
                System.out.println("请输入整数");
            }
        }

        reader.close();
        return list;
    }
}


class NumberUtil {
    /**
     * 获取int 型数组中最大值和最小值
     *
     * @param list 整数数组
     * @return int[] {max, min}
     */
    public static int[] getMaxMin(int[] list) {
        int max = list[0];
        int min = list[0];

        for (int x : list) {
            if (x > max) {
                max = x;
            }
            if (min > x) {
                min = x;
            }
        }
        return new int[]{max, min};
    }

}


class Demo {
    public static void main(String[] args) throws IOException {

        // 读取3个数据
        int[] list = InputUtil.getIntList(3);
        int[] data = NumberUtil.getMaxMin(list);

        System.out.println("最大值：" + data[0]);
        System.out.println("最小值：" + data[1]);

    }
}

92 文件保存

从键盘输入文件名和文件内容，然后将文件内容保存到文件中
1、定义接口
2、工具类
3、实现接口类
4、工厂类
5、测试函数

import java.io.*;


class InputUtil {
    private static final BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

    public static String getInput(String prompt) {

        System.out.println(prompt);
        String msg = null;

        while (true) {
            try {
                msg = reader.readLine();
                if (!"".equals(msg)) {
                    break;
                } else {
                    System.out.println("请输入非空字符串：");
                }
            } catch (IOException e) {

            }
        }
        return msg;
    }
}

interface IFileService {
    public static final String FILE_DIR = "demo";

    public boolean save();
}


class FileServiceImpl implements IFileService {

    private String filename;
    private String content;

    public FileServiceImpl() {
        this.filename = InputUtil.getInput("请输入文件名");
        this.content = InputUtil.getInput("请输入文件内容");
    }

    @Override
    public boolean save() {
        String fullname = this.FILE_DIR + File.separator + this.filename;

        PrintWriter writer = null;
        try {
            writer = new PrintWriter(fullname);
            writer.print(this.content);

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } finally {
            if (writer != null) {
                writer.close();
            }

        }
        return false;
    }
}


class Factory{
    private Factory(){}

    public static FileServiceImpl getInstance(){
        return new FileServiceImpl();

    }
}

class Demo {
    // 项目启动时创建文件夹
    static {
        File file = new File(IFileService.FILE_DIR);
        if (!file.exists()) {
            file.mkdirs();
        }
    }

    public static void main(String[] args) throws IOException {
        FileServiceImpl fileService = Factory.getInstance();
        fileService.save();
    }
}

93 字符串逆序显示

键盘传入多个字符串到程序中，并将它们按照逆序输出到屏幕

设计考虑：
1、字符串内容随时修改，使用StringBuffer
2、由用户自己决定是否继续输入

实现步骤
1、定义接口 操作标准
2、定义实现类
3、定义工厂类
4、编写辅助类
5、编写测试类

实现代码
IStringService.java

public interface IStringService {
    public void append(String str);
    public String[] reverse();
}

StringServiceImpl.java

public class StringServiceImpl implements IStringService{
    private StringBuffer data = new StringBuffer();

    public void append(String str){
        this.data.append(str).append("|");
    }

    public String[] reverse(){
        String[] list = this.data.toString().split("\\|");

        String[] tmp = new String[list.length];

        for(int i=0; i<list.length; i++){
            tmp[i] = list[list.length - i - 1];
        }

        return tmp;
    }
}

InputUtil.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class InputUtil {
    private static final BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

    public static String getString(String prompt) {

        System.out.println(prompt);
        String msg = null;

        while (true) {
            try {
                msg = reader.readLine();
                if (!"".equals(msg)) {
                    break;
                } else {
                    System.out.println("请输入非空字符串：");
                }
            } catch (IOException e) {

            }
        }
        return msg;
    }

    public static void main(String[] args) {
        System.out.println(InputUtil.getString("请输入"));
    }
}

Factory.java

class Factory{
    private Factory(){}

    public static StringServiceImpl getInstance(){
        return new StringServiceImpl();

    }
}

Menu.java

import java.util.Arrays;

public class Menu {
    private StringServiceImpl stringServiceImpl;

    public Menu() {
        this.stringServiceImpl = Factory.getInstance();
        this.choose();
    }

    public void choose() {
        help();

        String msg = InputUtil.getString("请选择：");
        switch (msg) {
            case "1":
                this.stringServiceImpl.append(InputUtil.getString("请输入字符串："));
                choose();

            case "2":
                System.out.println(Arrays.toString(this.stringServiceImpl.reverse()));
                choose();

                case "0":
                System.exit(0);

            default:
                choose();
        }

    }

    public static void help() {
        System.out.println("[1]输入内容：");
        System.out.println("[2]输出反转内容：");
        System.out.println("[0]退出");
    }
}

Demo.java

class Demo{
    public static void main(String[] args) {
        new Menu();
    }
}

94 数据排序处理

键盘输入数据 姓名:成绩|姓名:成绩

eg:

Tom:89|Jack:91|Tony:86

按照成绩由高到低排序

思路：
Comparable + Arrays

代码实现
IStudentService.java

public interface IStudentService {
    Student[] getData();
}

Student.java

public class Student implements Comparable<Student>{
    private String name;
    private double score;

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

    @Override
    public String toString() {
        return "Student<" +  name + ", " + score + '>';
    }

    @Override
    public int compareTo(Student obj) {
        return Double.compare(obj.score, this.score);
    }
}

StudentServiceImpl.java

import java.util.Arrays;

public class StudentServiceImpl implements IStudentService {
    private String content;
    private Student[] students;

    public StudentServiceImpl(String content) {
        this.content = content;
        this.handle();
    }

    private void handle(){
        String[] list = this.content.split("\\|");
        this.students = new Student[list.length];

        for(int i=0; i<list.length; i++){
            String[] items = list[i].split(":");
            this.students[i] = new Student(items[0], Double.parseDouble(items[1]));
        }
    }

    @Override
    public Student[] getData() {
        Arrays.sort(this.students);
        return this.students;
    }
}

Factory.java

public class Factory {
    private Factory(){}

    public static StudentServiceImpl getInstance(){
        return new StudentServiceImpl(InputUtil.getString("请输入数据："));
    }
}

Demo.java

import java.util.Arrays;

public class Demo {
    public static void main(String[] args) {
        // Tom:89|Jack:91|Tony:86
        System.out.println(Arrays.toString(Factory.getInstance().getData()));
        // [Student<Jack, 91.0>, Student<Tom, 89.0>, Student<Tony, 86.0>]
    }
}

95 数据排序处理深入

扩展上一节内容，将输入信息保存到文件中，还可以添加信息，并且查看全部数据

确认保存位置
格式统一

FileUtil.java文件读取工具类

package util;

import java.io.*;
import java.util.Scanner;

public class FileUtil {
    public static String read(File file) throws FileNotFoundException {
        Scanner scanner = new Scanner(file);
        StringBuilder contents = new StringBuilder();

        while (scanner.hasNext()) {
            contents.append(scanner.next());
        }

        scanner.close();

        return contents.toString();
    }

    public static void append(File file, String content) throws IOException {
        PrintWriter writer = new PrintWriter(new FileWriter(file, true));
        writer.write(content);
        writer.close();
    }

    public static void save(File file, String content) throws IOException {
        PrintWriter writer = new PrintWriter(file);
        writer.write(content);
        writer.close();
    }

    public static void main(String[] args) throws IOException {
        File file = new File("demo.txt");

        FileUtil.save(file, "你好");
        FileUtil.append(file, "你也好");
        System.out.println(FileUtil.read(file));
    }
}

96 奇偶数统计

输入字符串拆分后统计奇数，偶数个数

接口INumberService.java

public interface INumberService {
    public int[] handle();
}

实现类 NumberServiceImpl.java

import util.InputUtil;

public class NumberServiceImpl implements INumberService{
    private String str;

    public NumberServiceImpl(){
        this.str = InputUtil.getString("请输入数字串：");
    }

    @Override
    public int[] handle() {

        String[] numbers = this.str.split("");

        // 偶数， 奇数
        int[] result = new int[]{0, 0};
        for(String num : numbers){
            if(Integer.parseInt(num) % 2 == 0){
                result[0] ++;
            } else{
                result[1] ++;
            }
        }
        return result;
    }
}

测试类 Demo.java

import java.util.Arrays;

public class Demo {
    public static void main(String[] args) {
        System.out.println(Arrays.toString(new NumberServiceImpl().handle()));

        // 1234567890
        // [5, 5]
    }
}

97 用户登录

输入用户名和密码 root 123456
如果没有输入则提示输入
输入错误3次退出
提示登录成功

真实业务只实现核心功能，辅助逻辑处理交给代理控制

接口类
IUserService
isExit
login

实现类
UserServiceImpl

代理类
UserServiceProxy

工厂类
Factory

测试类
Demo

实现代码
IUserService.java

public interface IUserService {
    public boolean isExit();
    public boolean login(String name, String password);
}

UserServiceImpl.java

public class UserServiceImpl implements IUserService{
    private int tryCount = 0;

    @Override
    public boolean isExit() {
        // 超过三次错误
        return this.tryCount >= 3;
    }

    /**
     * 实现核心逻辑
     */
    @Override
    public boolean login(String name, String password) {
        this.tryCount ++;

        if("root".equals(name) && "123456".equals(password)){
            return true;
        } else{
            return false;
        }
    }
}

UserServiceProxy.java

import util.InputUtil;

public class UserServiceProxy implements IUserService {
    private IUserService userService;

    public UserServiceProxy(IUserService userService) {
        this.userService = userService;
    }

    @Override
    public boolean isExit() {
        return this.userService.isExit();
    }

    /**
     * 实现辅助逻辑
     */
    @Override
    public boolean login(String name, String password) {
        while (!this.isExit()) {
            String inputName = InputUtil.getString("请输入用户名：");
            String inputPassword = InputUtil.getString("请输入密码：");

            if (this.userService.login(inputName, inputPassword)) {
                System.out.println("登录成功");
                System.exit(0);
            } else {
                System.out.println("用户名或密码错误，请重试");
            }
        }

        System.out.println("重试次数过多，请稍后重试");
        return true;

    }
}

Factory.java

import util.InputUtil;

public class Factory {
    private Factory(){}

    public static IUserService getInstance(){
        return new UserServiceProxy(new UserServiceImpl());
    }
}

Demo.java

public class Demo {
    public static void main(String[] args) {
        Factory.getInstance().login(null, null);

    }
}

98 投票选举

1、输入候选人名单
2、统计每个候选人票数
3、显示最终投票结果
思路分析

1、定义数据结构：
Student
    name
    sid
    vote

2、操作接口类
IVoteService
    void inc(int sid)
    Student[] result() 排序数据
    Student[] getData() 未排序数据

3、实现类
VoteServiceImpl

4、工厂类
Factory

5、测试类
Demo

实现代码

数据结构 Student.java

public class Student implements Comparable<Student> {
    private String name;
    private int sid;
    private int vote;

    public Student(String name, int sid, int vote) {
        this.name = name;
        this.sid = sid;
        this.vote = vote;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getSid() {
        return sid;
    }

    public void setSid(int sid) {
        this.sid = sid;
    }

    public int getVote() {
        return vote;
    }

    public void setVote(int vote) {
        this.vote = vote;
    }

    @Override
    public int compareTo(Student obj) {
        return obj.vote - this.vote;
    }

    @Override
    public String toString() {
        return String.format("[%s] %s - %s", sid, name, vote);
    }
}

接口 IVoteService.java

public interface IVoteService {
    public void inc(int sid);

    public Student result();

    public Student[] getData();
}

实现类 VoteServiceImpl.java

import util.InputUtil;

import java.util.Arrays;

public class VoteServiceImpl implements IVoteService {
    private Student[] students;

    public VoteServiceImpl() {
        this.students = new Student[]{
                new Student("张三", 1, 0),
                new Student("李四", 2, 0),
                new Student("王五", 3, 0),
        };
    }

    @Override
    public void inc(int sid) {
        for(Student s : this.students){
            if(s.getSid() == sid){
                s.setVote(s.getVote() + 1);
            }
        }
    }

    @Override
    public Student result() {
        Arrays.sort(this.students);
        return this.students[0];
    }

    @Override
    public Student[] getData() {
        return this.students;
    }
}

工产类 Factory.java

public class Factory {
    private Factory(){}

    public static IVoteService getInstance(){
        return new VoteServiceImpl();
    }
}

菜单类 Menu.java

import util.InputUtil;

import java.util.Arrays;

public class Menu {
    private IVoteService voteService;

    public Menu() {
        this.voteService = Factory.getInstance();
        this.choose();
    }

    public void choose(){
        this.help();
        String num = InputUtil.getString("请选择：");

        switch (num){
            case "1":
                String sid = InputUtil.getString("请输入候选人id");
                this.voteService.inc(Integer.parseInt(sid));
                this.choose();
                break;
            case "2":
                System.out.println(Arrays.toString(this.voteService.getData()));
                this.choose();
                break;
            case "3":
                System.out.println(this.voteService.result());
                this.choose();
                break;
            case "0":
                System.out.println("拜拜...");
                System.exit(0);
            default:
                help();
                this.choose();
        }
    }

    public void help(){
        System.out.println("【1】候选人增加票数");
        System.out.println("【2】显示投票统计");
        System.out.println("【3】显示统计结果");
        System.out.println("【0】退出系统");
    }
}

测试类 Demo.java

public class Demo {
    public static void main(String[] args) {
        new Menu();
    }
}