我有一个包含5个客户(每行1个),Customer 1,Customer 2,Customer 3,Customer 4和Customer 5的文本文件。使用以下代码,它可以完美读取5行文本。
import java.io.*;
public class CustomerIO {
public void method () {
try (BufferedReader br = new BufferedReader(new FileReader(new File ("Customers.txt")))) {
int numberOfLines = readLines();
String [] text = new String [numberOfLines];
for (int i = 0; i < numberOfLines; i++) {
text[i] = br.readLine();
}
for (int i = 0; i < numberOfLines; i++) {
System.out.println(text[i]);
}
} catch (Exception e) {
e.printStackTrace();
}
private int readLines() {
try (BufferedReader br = new BufferedReader(new FileReader(new File ("Customers.txt")))) {
while ((line = br.readLine()) != null) {
numberOfLines++;
}
} catch (Exception e) {
e.printStackTrace();
}
return numberOfLines;
}
}
但是,当我更改为以下内容时,输出为:Customer 2,Customer 4,null
import java.io.*;
public class CustomerIO {
String line;
int numberOfLines = 0;
public void method () {
try (BufferedReader br = new BufferedReader(new FileReader(new File ("Customers.txt")))) {
while (br.readLine() != null) {
System.out.println(br.readLine());
}
} catch (Exception e) {
e.printStackTrace();
}
}
private int readLines() {
try (BufferedReader br = new BufferedReader(new FileReader(new File ("Customers.txt")))) {
while ((line = br.readLine()) != null) {
numberOfLines++;
}
} catch (Exception e) {
e.printStackTrace();
}
return numberOfLines;
}
}
主要方法包含在以下Runner.class文件中
public class Runner {
public static void main(String[] args) {
CustomerIO cus = new CustomerIO ();
cus.method();
}
}
您能帮我理解为什么会这样吗?我想在正确读取而不是使用String []时将客户读入arraylist。
谢谢
最佳答案
以下代码在循环的每次迭代中两次调用readLine()
,这就是为什么只看到其他每行的原因:
while (br.readLine() != null) {
System.out.println(br.readLine());
}
您需要将返回的值分配给变量,因此可以检查是否为空。
有很多方法可以做到这一点,所以我将按推荐的降序显示一些方法。
// Using for loop (recommended)
// Pro: Keeps the loop logic with the loop
// Limits the scope of the variable
// Smallest amount of code (lines of loop code: 2)
// Con: Unusual construct
// Inline assignment
for (String line; (line = br.readLine()) != null; ) {
System.out.println(line);
}
// Using while loop with inline assignment
// Pro: Common construct
// Keeps the loop logic with the loop
// Small amount of code (lines of loop code: 3)
// Con: Variable scope not limited to the loop
// Inline assignment
String line;
while ((line = br.readLine()) != null) {
System.out.println(line);
}
// Using while loop without inline assignment
// Pro: Common construct
// Con: Loop logic both before and at end of loop
// Variable scope not limited to the loop
// More code (lines of loop code: 4)
// Calling the readLine() method in two places
String line = br.readLine();
while (line != null) {
System.out.println(line);
line = br.readLine();
}
// Using break to exit forever loop
// Pro: Limits the scope of the variable
// Con: Loop logic both before and at end of loop
// Using infinite loop and the break statement
// More code (lines of loop code: 6)
for (;;) { // or: while (true)
String line = br.readLine();
if (line == null) {
break;
}
System.out.println(line);
}
关于java - 从文件中读取文本行,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/60048053/