Learned some basic knowledge of Java and wrote a super simple Notepad.
First of all, a large framework should be established. For example, Windows Notepad has the functions of creating a new file, opening a file, modifying a file, saving and so on. Without saying much, you can go directly to the code.
private static String filePath;
private static String message = "";
public static void main(String[] args) throws Exception {
Scanner scanner = new Scanner(System.in);
System.out.println("1: New file 2: open file 3: modify file 4: save 5: exit");
//create,open,modify,save,exit
while(true) {
System.out.println("Please enter instructions:");
int command = scanner.nextInt();
switch (command) {
case 1:
createFile();
break;
case 2:
openFile();
break;
case 3:
modifyFile();
break;
case 4:
saveFile();
break;
case 5:
exit();
break;
default:
System.out.println("The command you entered is wrong( one-5)");
break;
}
}
}
I don't know how to describe some specific points to make them easy to understand. Anyway, after learning, I know how to write like this. I didn't search the Internet for how others wrote it. This should be the simplest.
Next, there are several small frameworks. I won't say much more. After running all the code, the operation is very simple. You should be able to start directly after reading it.
new file
private static void createFile() {
message = "";
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter the content and enter it when stopping\"stop\":");
StringBuffer sBuffer = new StringBuffer();
String inputMessage = "";
while (!inputMessage.equals("stop")) {
if (sBuffer.length()>0) {
sBuffer.append("\r\n");
}
sBuffer.append(inputMessage);
inputMessage = scanner.nextLine();
}
message = sBuffer.toString();
}
Open file
private static void openFile() throws Exception {
message = "";
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter the location of the open file:");
filePath = scanner.next();
if (filePath != null && !filePath.endsWith(".txt")) {
System.out.println("Please select a text file!");
return;
}
FileReader in = new FileReader(filePath);
char[]charArray = new char[1024];
int len = 0;
StringBuffer sb = new StringBuffer();
while((len = in.read(charArray)) != -1) {
sb.append(charArray);
}
message = sb.toString();
System.out.println("Open file contents:"+"\r\n" + message);
in.close();
}
Modify file
private static void modifyFile() {
if (message == "" && filePath ==null) {
System.out.println("Please create a new file or open it first");
return;
}
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter the content to be modified (in Chinese)\"Modified target text: modified text\")," + "Stop modifying, please enter\"stop\":");
String inputMessage = "";
while(!inputMessage.equals("stop")) {
inputMessage = scanner.nextLine();
if (inputMessage != null && inputMessage.length() > 0) {
String[] modifyMessage = inputMessage.split(":");
if (modifyMessage != null && modifyMessage.length > 1) {
message = message.replace(modifyMessage[0], modifyMessage[1]);
}
}
}
System.out.println("Modified content:" + "\r\n" + message);
}
Save file
private static void saveFile() throws IOException {
Scanner scanner = new Scanner(System.in);
FileWriter out = null;
if (filePath != null) {
out = new FileWriter(filePath);
}else {
System.out.println("Please enter the absolute path to save the file:");
String path = scanner.next();
filePath = path;
if (!filePath.toLowerCase().endsWith(".txt")) {
filePath += ".txt";
}
out = new FileWriter(filePath);
}
out.write(message);
out.close();
message = "";
filePath = null;
}
sign out
private static void exit() {
System.out.println("You have exited the system, thank you for using!");
System.exit(0);
}
Some methods used in the code must be imported into the package, and then the complete code.
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
public class Notepad {
private static String filePath;
private static String message = "";
public static void main(String[] args) throws Exception {
Scanner scanner = new Scanner(System.in);
System.out.println("1: New file 2: open file 3: modify file 4: save 5: exit");
while(true) {
System.out.println("Please enter instructions:");
int command = scanner.nextInt();
switch (command) {
case 1:
createFile();
break;
case 2:
openFile();
break;
case 3:
modifyFile();
break;
case 4:
saveFile();
break;
case 5:
exit();
break;
default:
System.out.println("The command you entered is wrong( one-5)");
break;
}
}
}
private static void createFile() {
message = "";
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter the content and enter it when stopping\"stop\":");
StringBuffer sBuffer = new StringBuffer();
String inputMessage = "";
while (!inputMessage.equals("stop")) {
if (sBuffer.length()>0) {
sBuffer.append("\r\n");
}
sBuffer.append(inputMessage);
inputMessage = scanner.nextLine();
}
message = sBuffer.toString();
}
private static void openFile() throws Exception {
message = "";
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter the location of the open file:");
filePath = scanner.next();
if (filePath != null && !filePath.endsWith(".txt")) {
System.out.println("Please select a text file!");
return;
}
FileReader in = new FileReader(filePath);
char[]charArray = new char[1024];
int len = 0;
StringBuffer sb = new StringBuffer();
while((len = in.read(charArray)) != -1) {
sb.append(charArray);
}
message = sb.toString();
System.out.println("Open file contents:"+"\r\n" + message);
in.close();
}
private static void modifyFile() {
if (message == "" && filePath ==null) {
System.out.println("Please create a new file or open it first");
return;
}
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter the content to be modified (in Chinese)\"Modified target text: modified text\")," + "Stop modifying, please enter\"stop\":");
String inputMessage = "";
while(!inputMessage.equals("stop")) {
inputMessage = scanner.nextLine();
if (inputMessage != null && inputMessage.length() > 0) {
String[] modifyMessage = inputMessage.split(":");
if (modifyMessage != null && modifyMessage.length > 1) {
message = message.replace(modifyMessage[0], modifyMessage[1]);
}
}
}
System.out.println("Modified content:" + "\r\n" + message);
}
private static void saveFile() throws IOException {
Scanner scanner = new Scanner(System.in);
FileWriter out = null;
if (filePath != null) {
out = new FileWriter(filePath);
}else {
System.out.println("Please enter the absolute path to save the file:");
String path = scanner.next();
filePath = path;
if (!filePath.toLowerCase().endsWith(".txt")) {
filePath += ".txt";
}
out = new FileWriter(filePath);
}
out.write(message);
out.close();
message = "";
filePath = null;
}
private static void exit() {
System.out.println("You have exited the system, thank you for using!");
System.exit(0);
}
}
After running, I can see this on the console. Let me also make a simple operation.
Create a new one first.
After entering the content, press enter and enter stop to end.
Then save and try.
This error occurs because there is no java folder in my D disk and the specified directory cannot be found. It can only be saved as a txt file.
So I created a new java folder on disk D and ran without error.
Then go to disk D and look for it.
Try the open function again.
You can't enter D:\java\one here. Of course, you need a file suffix to open the file.
I also searched it myself. The Notepad written by many big guys is much more advanced than mine. I should be able to write it for java beginners.