停止讀取某一行的文本文件java

Question

在我的程序塊中，我試圖獲取用戶輸入並將它與文件「PriceList3.txt」中的每一行進行比較。對於每一行，我都存儲了一些字符串變量。當其中一行的某些內容與用戶輸入（contains方法）相同時，我使用Pattern和Matcher類來提取某些信息，並將txt文件的一行部分分配給一個變量。在我調用setPrice方法後，我試圖停止閱讀「PriceList3.txt」文件。當if（m.find（））中的所有語句都被執行後，您是否知道如何停止讀取文件？我不知道從哪裏開始。

感謝您的回覆和幫助。

String regularExpr = "([\\w]+)\\s+([\\w]+)\\s+([\\d.\\d)]+)[\\D]+([\\d.\\d]+)"; 
Pattern pattern = Pattern.compile(regularExpr); 
File inFile = new File("PriceList3.txt"); 
Scanner read = new Scanner(inFile); 
System.out.print("Enter the name and weight of the item: "); 
String item = scan.nextLine(); 
while(read.hasNextLine()) 
{ 
    String each = read.nextLine(); 
    if(each.contains(item)) 
    { 
     Matcher m = pattern.matcher(each); 
     if(m.find()) 
     { 
      String itemName1 = m.group(1).trim()+ " " + m.group(2); 
      itemName.setName(itemName1); 
      String weight = (m.group(3).trim()); 
      double weight1 = Double.parseDouble(weight); 
      itemName.setWeight(weight1); 
      double itemPrice = Double.parseDouble(m.group(4).trim()); 
      itemName.setPrice(itemPrice); 
     } 
     cashier1.addItem(itemName); 
    } 
} 

Answer 1

你可以使用break語句作爲@Neil寫，或者你可以檢查，而檢查的一些變量：

boolean stop = false; 
while(read.hasNextLine() && !stop) { 
... 
//if you want to stop 
stop = true; 

} 

Answer 2

如果你想停止while循環，最簡單的是將加休息;

String regularExpr = "([\\w]+)\\s+([\\w]+)\\s+([\\d.\\d)]+)[\\D]+([\\d.\\d]+)"; 
Pattern pattern = Pattern.compile(regularExpr); 
File inFile = new File("PriceList3.txt"); 
Scanner read = new Scanner(inFile); 
System.out.print("Enter the name and weight of the item: "); 
String item = scan.nextLine(); 
while(read.hasNextLine()) 
{ 
    String each = read.nextLine(); 
    if(each.contains(item)) 
    { 
     Matcher m = pattern.matcher(each); 
     if(m.find()) 
     { 
      String itemName1 = m.group(1).trim()+ " " + m.group(2); 
      itemName.setName(itemName1); 
      String weight = (m.group(3).trim()); 
      double weight1 = Double.parseDouble(weight); 
      itemName.setWeight(weight1); 
      double itemPrice = Double.parseDouble(m.group(4).trim()); 
      itemName.setPrice(itemPrice); 
      //Jumps out of the innerst loop 
      break; 
     } 
     cashier1.addItem(itemName); 
    } 
} 
//if break is called, the code will continue at this line 

雖然有些人可能會爭辯說破環是不是很好（因爲你在代碼中跳來跳去，它可以成爲大型項目的混亂）。另一種方法是添加布爾值

String regularExpr = "([\\w]+)\\s+([\\w]+)\\s+([\\d.\\d)]+)[\\D]+([\\d.\\d]+)"; 
Pattern pattern = Pattern.compile(regularExpr); 
File inFile = new File("PriceList3.txt"); 
Scanner read = new Scanner(inFile); 
System.out.print("Enter the name and weight of the item: "); 
String item = scan.nextLine(); 
//add the boolean 
boolean complete = false; 
//stops the loop once complete is false 
while(read.hasNextLine() && !complete) 
{ 
    String each = read.nextLine(); 
    if(each.contains(item)) 
    { 
     Matcher m = pattern.matcher(each); 
     if(m.find()) 
     { 
      String itemName1 = m.group(1).trim()+ " " + m.group(2); 
      itemName.setName(itemName1); 
      String weight = (m.group(3).trim()); 
      double weight1 = Double.parseDouble(weight); 
      itemName.setWeight(weight1); 
      double itemPrice = Double.parseDouble(m.group(4).trim()); 
      itemName.setPrice(itemPrice); 
      //Sets the boolean 
      complete = true; 
     } 
     //only adds the item if complete is false 
     if(!complete){ 
      cashier1.addItem(itemName); 
     } 
    } 
}