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Problems encountered in special flow & properties property set instances and Solutions
2022-07-29 02:16:00 【Wang Xiaoya】
Catalog
stem 1：
Write a small program , Record the number of times the program runs , Satisfy 5 Next time , Give hints , The number of trials has reached , Please register ！
analysis ：
1. Encapsulate the configuration file as File object , Judge whether the file exists , If it doesn't exist, create it yourself
2. A counter is required ;
3. The value of the counter , The life cycle is longer than the application life cycle , You need to persist the value of the counter .count = 1, What is stored inside should be the key value method ,Map aggregate , To be associated with the data on the device , need IO technology . aggregate + IO = Properties.
Their thinking ：
1. Write a small program class , Take guessing numbers as an example , stay 1-100 Randomly generate an arbitrary natural number , Input the numbers in turn and compare them to generate numbers , Correct answer exit , Once ;
System.out.println(" Please enter a number （1-100）:");
int number=sc.nextInt();// Used to receive the numbers entered by the console
// Only jump out of the loop when you guess right , Program end
while(true){
if (number < i) {
System.out.println("sorry, You guess it's small ");
} else if (number > i) {
System.out.println("sorry, You guessed big ");
} else if (number==i){
System.out.println(" congratulations , bingo ");
break;
}
System.out.println(" Please enter a number :");
number=sc.nextInt();
}2. Create a data source directory File object , The path is a Temp\\applet.txt, Judge whether the file exists , If it doesn't exist, create it yourself ;
File file = new File("E:\\IdeaProjects\\firstProject\\Temp\\applet.txt");
if (!file.exists()) {
file.createNewFile();// create a file
}3. Once it's created applet.txt Remember to write the initialization object into the file later count=0（ Remember that ！！！）
4. Read data from file to Properties aggregate , use load() Method realization ;
FileReader fr = new FileReader("E:\\IdeaProjects\\firstProject\\Temp\\applet.txt");
// Read data from file to Properties aggregate , use load() Method realization
Properties prop = new Properties();// Read the attribute list from the input character stream （ Bond and element pair ）
prop.load(fr);
fr.close(); // Release resources 5. Determine whether the number of times has reached 5 Time ,
If it comes to , Give hints ： The number of trials has reached , Please register ！
If not, you can continue to run
// Determine whether the number of times has reached 5 Time
if (number >= 5) {
// If it comes to , Give hints ： The number of trials has reached , Please register ！
System.out.println(" The number of trials has reached , Please register ！");
} else {
// Can continue to run
Running02 running = new Running02();
running.start();
}6. Run once +1, Write back the file , use Properties Of store() Method realization
// frequency +1, Write back the file , use Properties Of store() Method realization
number++;
prop.setProperty("count", String.valueOf(number));
FileWriter fw = new FileWriter("Temp\\applet.txt");
prop.store(fw, null);
fw.close();Problems and solutions ：
problem 1： Run and exit directly , Report errors
reason ：if Statement area error
solve ： take “}” Just put it in the right place
problem 2：
reason ：
prop.load(fr); Release resources before writing , Nature is null, Error string conversion type error , Write the content and it will work normally
solve ：
problem 3： Can't read data
reason ：applet.txt There are no initialization times in the file count
solve ： Write initialization object count=0
matters needing attention ：
1. At first I tried to use FileReader Create a data source directory File object , But I made a mistake in judging whether the file exists , Find out File.exists() More convenient , So I changed the code ,
First create File Object reuse File.exists() Judge whether it exists ,
If it does not exist, use file.createNewFile() create a file ,
Then write the newly created FileReader In the object
File file = new File("E:\\IdeaProjects\\firstProject\\Temp\\applet.txt");
if (!file.exists()) {
file.createNewFile();// create a file
}
FileReader fr = new FileReader("E:\\IdeaProjects\\firstProject\\Temp\\applet.txt");
// Read data from file to Properties aggregate , use load() Method realization
Properties prop = new Properties();// Read the attribute list from the input character stream （ Bond and element pair ）
prop.load(fr);
fr.close(); // Release resources 2. Once it's created applet.txt Remember to write the initialization object into the file later count=0（ Remember that ！！！）
Running results ：
Complete code ：
Operation class ：
package com.B.IOStream_14.Properties;
import java.util.Random;
import java.util.Scanner;
// The class that runs the code
public class Running02 {
public static void start() {
// Generate a 1~100 The random number
Random r=new Random();
int i=r.nextInt(100);
// Enter the guessed number on the keyboard
Scanner sc=new Scanner(System.in);
System.out.println(" Please enter a number （1-100）:");
int number=sc.nextInt();// Used to receive the numbers entered by the console
// Only jump out of the loop when you guess right , Program end
while(true){
if (number < i) {
System.out.println("sorry, You guess it's small ");
} else if (number > i) {
System.out.println("sorry, You guessed big ");
} else if (number==i){
System.out.println(" congratulations , bingo ");
break;
}
System.out.println(" Please enter a number :");
number=sc.nextInt();
}
}
}
Test class ：
package com.B.IOStream_14.Properties;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Properties;
//2. Write a small program , Record the number of times the program runs , Satisfy 5 Next time , Give hints , The number of trials has reached , Please register ！
// analysis ：
// 1. Encapsulate the configuration file as File object , Judge whether the file exists , If it doesn't exist, create it yourself
// 2. A counter is required ;
// 3. The value of the counter , The life cycle is longer than the application life cycle , You need to persist the value of the counter .
// count = 1, What is stored inside should be the key value method ,Map aggregate , To be associated with the data on the device , need IO technology .
// aggregate + IO = Properties
public class A2 {
public static void main(String[] args) throws IOException {
// Create a data source directory File object , The path is a Temp\applet.txt
File file = new File("E:\\IdeaProjects\\firstProject\\Temp\\applet.txt");
if (!file.exists()) {
file.createNewFile();// create a file
}
FileReader fr = new FileReader("E:\\IdeaProjects\\firstProject\\Temp\\applet.txt");
// Read data from file to Properties aggregate , use load() Method realization
Properties prop = new Properties();// Read the attribute list from the input character stream （ Bond and element pair ）
prop.load(fr);
fr.close(); // Release resources
// adopt Properties Set to get the number of games played
String count = prop.getProperty("count");
int number = Integer.parseInt(count);
// Determine whether the number of times has reached 5 Time
if (number >= 5) {
// If it comes to , Give hints ： The number of trials has reached , Please register ！
System.out.println(" The number of trials has reached , Please register ！");
} else {
// Can continue to run
Running02 running = new Running02();
running.start();
}
// frequency +1, Write back the file , use Properties Of store() Method realization
number++;
prop.setProperty("count", String.valueOf(number));
FileWriter fw = new FileWriter("Temp\\applet.txt");
prop.store(fw, null);
fw.close();
}
}stem 2：
Use code to realize the following requirements
(1) Define the student class , Include name (String name), Gender (String gender), Age (int age) Three attributes , Generate null and parametric constructions ,set and get Method ,toString Method
(2) Keyboard Entry 6 Student information ( Input format : Zhang San , male ,25), Two identical messages are required , take 6 Student information is stored in ArrayList Collection
(3) There will be 6 Student information ArrayList The collection object is written to D:\\StudentInfo.txt In file
(4) Read D:\\StudentInfo.txt In the document ArrayList object
(5) Yes ArrayList In the collection 6 Students were de duplicated and sorted in order of age
(6) take ArrayList The sorted results in the set are used PrintWriter Stream write to E:\\StudentInfo.txt In file ( Write format ： Zhang San - male -25)
Their thinking ：
1. Define the student class , Include name (String name), Gender (String gender), Age (int age) Three attributes , Generate null and parametric constructions ,set and get Method ,toString Method ;
private String name;
private String gender;
private int age;
public Student03() {
}
public Student03(String name, String gender, int age) {
this.name = name;
this.gender = gender;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Student03{" +
"name='" + name + '\'' +
", gender='" + gender + '\'' +
", age=" + age +
'}';2. Create a collection object
ArrayList<Student03> array = new ArrayList<Student03>();
3. Enter the data required by the student object with the keyboard
// Enter the data required by the student object with the keyboard
Scanner sc = new Scanner(System.in);
System.out.println(" Please enter the student's name :");
String name = sc.nextLine();
System.out.println(" Please enter the student's gender :");
String gender = sc.nextLine();
System.out.println(" Please enter the age of the student :");
int age = sc.nextInt();4. Create student objects , Assign the data entered by the keyboard to the member variables of the student object , Add a student object to the collection
Student03 s = new Student03();
s.setName(name);
s.setGender(gender);
s.setAge(age);
// Add a student object to the collection
array.add(s);5. There will be 6 Student information ArrayList The collection object is written to StudentInfo.txt file
FileWriter fw = new FileWriter(new File("Temp\\StudentInfo.txt"));
for (Student03 stu03 : array) {
fw.write(String.valueOf(stu03));
fw.flush();
}
System.out.println(" Copy complete !");
fw.close();
6. In order to improve the reusability of code , We use methods to call methods addStudent, Ergodic set , The general traversal format is used to realize
// In order to improve the reusability of code , We use methods to call methods addStudent
for (int i =0; i<6;i++){
addStudent(array);
}
// 6: Ergodic set , The general traversal format is used to realize
for (int i = 0; i < array.size(); i++) {
Student03 s = array.get(i);
System.out.println(s.getName() + ","+s.getGender()+"," + s.getAge());
}
}
What happened ：
problem 1： Enter name, gender and age , Output name and age of results , Gender loss
But look at the constructed StudentInfo There is gender in it , Strange ！
reason ： Solved the case ！ When traversing the output, it is not added orz……
solve ：
Running results ：
Complete code ：
Students ：
package com.B.IOStream_14.Properties;
//3. Use code to realize the following requirements
//(1) Define the student class , Include name (String name), Gender (String gender), Age (int age) Three attributes , Generate null and parametric constructions ,set and get Method ,toString Method
//(2) Keyboard Entry 6 Student information ( Input format : Zhang San , male ,25), Two identical messages are required , take 6 Student information is stored in ArrayList Collection
//(3) There will be 6 Student information ArrayList The collection object is written to D:\\StudentInfo.txt In file
//(4) Read D:\\StudentInfo.txt In the document ArrayList object
//(5) Yes ArrayList In the collection 6 Students were de duplicated and sorted in order of age
//(6) take ArrayList The sorted results in the set are used PrintWriter Stream write to E:\\StudentInfo.txt In file ( Write format ： Zhang San - male -25)
public class Student03 {
private String name;
private String gender;
private int age;
public Student03() {
}
public Student03(String name, String gender, int age) {
this.name = name;
this.gender = gender;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Student03{" +
"name='" + name + '\'' +
", gender='" + gender + '\'' +
", age=" + age +
'}';
}
}
Test class ：
package com.B.IOStream_14.Properties;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Scanner;
//3. Use code to realize the following requirements
//(1) Define the student class , Include name (String name), Gender (String gender), Age (int age) Three attributes , Generate null and parametric constructions ,set and get Method ,toString Method
//(2) Keyboard Entry 6 Student information ( Input format : Zhang San , male ,25), Two identical messages are required , take 6 Student information is stored in ArrayList Collection
//(3) There will be 6 Student information ArrayList The collection object is written to D:\\StudentInfo.txt In file
//(4) Read D:\\StudentInfo.txt In the document ArrayList object
//(5) Yes ArrayList In the collection 6 Students were de duplicated and sorted in order of age
//(6) take ArrayList The sorted results in the set are used PrintWriter Stream write to E:\\StudentInfo.txt In file ( Write format ： Zhang San - male -25)
public class A3 {
public static void main(String[] args) throws IOException {
// Create objects
ArrayList<Student03> array = new ArrayList<Student03>();
// In order to improve the reusability of code , We use methods to call methods addStudent
for (int i =0; i<6;i++){
addStudent(array);
}
// 6: Ergodic set , The general traversal format is used to realize
for (int i = 0; i < array.size(); i++) {
Student03 s = array.get(i);
System.out.println(s.getName() + ","+s.getGender()+"," + s.getAge());
}
}
/*
Two clear ：
return type ：void
Parameters ：ArrayList<Student03> array
*/
public static void addStudent (ArrayList<Student03> array) throws IOException {
// Enter the data required by the student object with the keyboard
Scanner sc = new Scanner(System.in);
System.out.println(" Please enter the student's name :");
String name = sc.nextLine();
System.out.println(" Please enter the student's gender :");
String gender = sc.nextLine();
System.out.println(" Please enter the age of the student :");
int age = sc.nextInt();
// Create student objects , Assign the data entered by the keyboard to the member variables of the student object
Student03 s = new Student03();
s.setName(name);
s.setGender(gender);
s.setAge(age);
// Add a student object to the collection
array.add(s);
// There will be 6 Student information ArrayList The collection object is written to D:\\StudentInfo.txt In file
FileWriter fw = new FileWriter(new File("Temp\\StudentInfo.txt"));
for (Student03 stu03 : array) {
fw.write(String.valueOf(stu03));
fw.flush();
}
System.out.println(" Copy complete !");
fw.close();
}
}
Last thing I want to say ：
Writing code seems simple but not simple , Many times, small details that seem inconspicuous can often determine success or failure , My life is boundless, but my study is boundless , Work hard together to refuel ！
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