練習掃描文件

Question

我必須打印此文件的「文本」的偶數行，我該怎麼做？

public static void main(String[] args) throws FileNotFoundException{ 
    File f =new File("text.txt"); 
    Scanner scanner = new Scanner(f); 

    while(scanner.hasNextLine()){ 
     System.out.println(scanner.nextLine()); 
    } 
} 

謝謝。

Answer 1

下面是一個簡單的方法來跟蹤哪些行你是如何判斷它是偶數或沒有。如果它的確是一個偶數，那麼我們就打印它。

public static void main(String[] args) throws FileNotFoundException { 
    File f = new File("text.txt"); 
    Scanner scanner = new Scanner(f); 
    int counter = 1; //This will tell you which line you are on 

    while(scanner.hasNextLine()) { 
     if (counter % 2 == 0) { //This checks if the line number is even 
      System.out.println(scanner.nextLine()); 
     } 
     counter++; //This says we just looked at one more line 
    } 
} 

Answer 2

使用上線人數remainder operator %在遍歷文件內容

Answer 3

你也可以消耗每while循環迭代兩個標記並打印出每一個第一（偶數）之一。

雖然使用計數器可能更清晰。

import java.util.Scanner; 
import java.io.File; 
import java.io.FileNotFoundException; 

public class NumberPrinter { 
    public static void main(String[] args) throws FileNotFoundException{ 
    File f =new File("text.txt"); 
    Scanner scanner = new Scanner(f); 

    while(scanner.hasNextLine()){ 
     System.out.println(scanner.nextLine()); 
     if (scanner.hasNextLine()) { 
     scanner.nextLine(); 
     } 
    } 
    } 
}