將Instrument類方法的輸出寫入用戶從命令行參數輸入的文本文件

Question

我正在學習Java初級編程課程，目前我正在研究最終項目。可以在這裏找到作業說明link

我很難完成此任務「將輸出從Instrument類方法寫入用戶從命令行參數輸入的文本文件（例如，java Mynamep3tst myfilename.txt ）「。這裏是我的一些代碼：

import java.io.*; 

public class Test{ 

public static void main(String[] args) { 

    String outputFile = ""; 
    if (0 < args.length) { 
     outputFile = args[0]; 
     System.out.println("This program will write output to this file: " + outputFile + "\n"); 

    try { 

     File file = new File(outputFile); 

     PrintWriter output = new PrintWriter(outputFile); 

     output.println("hello"); //to check if ir prints anything 

     Violin[] simpleViolin = new Violin[5]; 

    //Create 5 violin objects 
    for (int i = 0; i < simpleViolin.length; i++){ 
     simpleViolin[i] = new Violin(); 
    } 

    output.println("\nLet's tune " + Violin.getNumberOfViolins() + " violins."); 
    for(int i = 0; i < simpleViolin.length; i++){ 
     output.print(i + 1); 
     simpleViolin[i].tuneOn(); 
    } 

    output.println("\nNow let's start playing " + Violin.getNumberOfViolins() + " violins."); 
    for(int i = 0; i < simpleViolin.length; i++){ 
     output.print(i + 1); 
     simpleViolin[i].startPlaying(); 
    } 

    output.println("\nIt looks like " + Violin.getNumberOfViolins() + " violins have untuned."); 
    for(int i = 0; i < simpleViolin.length; i++){ 
     output.print(i + 1); 
     simpleViolin[i].tuneOff(); 
    } 

    output.println("\nThis music is terrible! Let's stop it!"); 
    for(int i = 0; i < simpleViolin.length; i++){ 
     output.print(i + 1); 
     simpleViolin[i].stopPlaying(); 
    } 

     output.close(); 

    } 

    catch (IOException io){ 

     System.out.println("Sorry that file is not found " + io); 

    } 
    }//end if 

    }//end main 

}//end Test 

class Violin{ 
private final int numberOfStrings = 4; 
private final char[] stringNames = {'E', 'A', 'D', 'G'}; 
private boolean isTuned = false; 
private boolean isPlaying = false; 
private static int numberOfViolins = 0; 
private PrintWriter output; 

public Violin(){ 
    numberOfViolins++; 
} 

public void startPlaying() { 
    isPlaying = true; 
    System.out.println(" violin is now playing."); 
} 

public void stopPlaying() { 
    isPlaying = false; 
    System.out.println(" violin has stopped playing."); 
} 

public void tuneOn() { 
    isTuned = true; 
    System.out.println(" violin is now tuned."); 
} 

public void tuneOff() { 
    isTuned = false; 
    System.out.println(" violin is untuned."); 
} 

static int getNumberOfViolins(){ 
    return numberOfViolins; 
} 
}//end class Violin 

所以我的問題是如何讓我的小提琴類方法打印到用戶指定的文件？

Answer 1

當您創建小提琴對象時，您可以將輸出作爲參考傳遞給構造函數，因此在小提琴內部您將使用輸出而不是System.out.println。

更改Violoin構造函數：

，然後只用小提琴內部outpu。