Java学习路线-28：JavaIO编程案例
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, Student, Student]
}
}
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();
}
}