[英]Can not get java to write to a text file using PrintWriter
让我以说我对Java极其陌生为序。 这是我上课的第八周,我被困在一个项目上。 这是我到目前为止的内容:
import java.io.*;
public class Guitar {
// Initialize variables
boolean isPlaying;
boolean inTune;
char[] guitStrings = {'D', 'G', 'C', 'A'}; // Guitar strings
int numOfStrings = 4; // Number of strings the guitar has.
public void Guitar(){
isPlaying = false; // Guitar is not playing by default.
inTune = false; // Guitar is not tuned by default.
System.out.println("The guitar is not tuned and is not playing.");
}
public void isPlaying(){
System.out.println("Your guitar is now playing!");
isPlaying = true; // Set guitar to playing
}
public void inTune(){
System.out.println("Your guitar is now tuned!");
inTune = true; // Set guitar to tuned.
}
public void stopPlaying(){
isPlaying = false; // Set isPlaying to false.
System.out.println("Your guitar has finished playing!");
}
public void notes(){
System.out.println("The guitar has played a total of " + numOfStrings +
" strings and they are: " + guitStrings[0] + "," + guitStrings[1] + ","
+ guitStrings[2] + "," + guitStrings[3]);
}
public static void main(String[] args) throws IOException{
java.io.File file = new java.io.File("guitartest.txt");
if(file.exists()){
System.out.println("File already exists!");
System.exit(1);
}
// Create a file
java.io.PrintWriter output = new java.io.PrintWriter(file);
Guitar[] guit = new Guitar[10];
for (int i = 0; i < guit.length; i++){
guit[i] = new Guitar();
guit[i].Guitar();
guit[i].inTune();
guit[i].isPlaying();
guit[i].notes();
guit[i].stopPlaying();
}
}
}
该程序可以完成我需要做的所有事情,但是我们在项目上还有最后一步。 我必须从命令行将其输出到文本文件。 我将最后的代码更改为此:
public static void main(String[] args) throws IOException{
java.io.File file = new java.io.File("guitartest.txt");
if (file.exists()){
System.out.println("This file already exists!");
System.exit(1);
}
// Create a file
java.io.PrintWriter output = new java.io.PrintWriter(file);
Guitar[] guit = new Guitar[10]; // Create 10 instruments
for (int i = 0; i < guit.length; i++){
output.println(guit[i] = new Guitar());
output.println(guit[i].Guitar());
output.println(guit[i].inTune());
output.println(guit[i].isPlaying());
output.println(guit[i].notes());
output.println(guit[i].stopPlaying());
}
}
这将编译代码,并在控制台中显示我想要的结果,但是文本文件guitartest.txt完全空白。 我不是在寻找别人为我完成这项任务,而是在寻找您可以向我提供的任何建议或资源。 非常感谢你!
PrintWriter被缓冲,这意味着您要写入的文本在实际写入文件之前已存储在其内部缓冲区中。 因此,完成写入后,您需要调用close()方法,以便PrintWriter对象将数据写入文件并关闭它。
您也可以调用flush(),如果您想立即写入数据但又想继续使用PrintWriter对象,这可能会很有用。
写完之后
output.flush();
output.close();
接受File
的PrintWriter
构造函数实现为
public PrintWriter(File file) throws FileNotFoundException {
this(new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file))),
false);
}
换句话说,您的输出正在缓冲中,需要不时刷新或一次刷新。
呼叫
output.flush();
要么
output.close();
使用完后。
您可能需要在末尾刷新输出流,即在main()
方法中的for
循环之后执行
output.flush();
output.close();
为了安全起见,可以将这两个调用都包含在try/catch
块中:
try {
output.flush();
output.close();
} catch (Exception e) {
e.printStackTrace();
}
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