花几千上万学习Java，真没必要！（三十九）

1、BufferedReader的使用：

测试代码：

package test.com;
import java.io.BufferedReader;  
import java.io.FileReader;  
import java.io.IOException;  
import java.util.ArrayList;  
import java.util.List;  public class FileReadToList {  public static void main(String[] args) {  // 文件路径  String filePath = "D:\\AA\\a.txt";  // 创建列表存储文件中的每一行  List<String> lines = new ArrayList<>();  try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {  String line;  // 逐行读取直到文件末尾  while ((line = reader.readLine()) != null) {  // 将读取的每一行添加到列表中  lines.add(line);  }  // 遍历列表并打印每一行  for (String str : lines) {  System.out.println(str);  }  } catch (IOException e) {  e.printStackTrace();  System.out.println("读取文件时发生错误：" + e.getMessage());  }  }  
}

运行结果如下;

2、BufferedWriter的使用：

测试代码：

package test.com;
import java.io.BufferedWriter;  
import java.io.FileWriter;  
import java.io.IOException;  
import java.util.ArrayList;  
import java.util.List;  public class WriteListToFile {  public static void main(String[] args) {  // ArrayList集合，存储字符串。  List<String> strings = new ArrayList<>();  strings.add("第一行");  strings.add("第二行");  strings.add("第三行");  // 指定文件路径  String filePath = "E:\\Test\\a.txt";  // 使用try-with-resources语句来自动关闭BufferedWriter  try (BufferedWriter writer = new BufferedWriter(new FileWriter(filePath))) {  // 遍历集合  for (String str : strings) {  // 将每个字符串写入文件，并在末尾添加换行符  writer.write(str);  writer.newLine(); // 写入一个新的行分隔符  }  // 由于使用了try-with-resources，不需要显式调用writer.close();  // 会在try块的末尾自动调用  } catch (IOException e) {  e.printStackTrace();  System.out.println("写入文件时发生错误：" + e.getMessage());  }  System.out.println("文件写入完成。");  }  
}

运行结果如下：

3、文件到集合：

测试代码：

创建一个运动员类;

package test.com; 
public class Athlete {  private String name;  private String gender;  private String nationality;  private double height; // 身高，单位cm  private double weight; // 体重，单位kg  // 构造方法public Athlete(String name, String gender, String nationality, double height, double weight) {  this.name = name;  this.gender = gender;  this.nationality = nationality;  this.height = height;  this.weight = weight;  }   public String getName() {return name;}public void setName(String name) {this.name = name;}public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}public String getNationality() {return nationality;}public void setNationality(String nationality) {this.nationality = nationality;}public double getHeight() {return height;}public void setHeight(double height) {this.height = height;}public double getWeight() {return weight;}public void setWeight(double weight) {this.weight = weight;}// toString方法（可选，用于打印Athlete对象的信息）  @Override  public String toString() {  return "Athlete{" +  "name='" + name + '\'' +  ", gender='" + gender + '\'' +  ", nationality='" + nationality + '\'' +  ", height=" + height + "cm" +  ", weight=" + weight + "kg" +  '}';  }  
}

读取：E:\\Test\\athletes.txt 文本中的文件到集合：

package test.com;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;public class RandomRollCall {public static void main(String[] args) {List<Athlete> athletes = new ArrayList<>();BufferedReader reader = null;try {reader = new BufferedReader(new FileReader("E:\\Test\\athletes.txt"));String line;while ((line = reader.readLine()) != null) {String[] fields = line.split("\\s+"); // 使用一个或多个空格作为分隔符if (fields.length >= 4) {String name = fields[0];String gender = fields[1];String nationality = fields[2];// 去除身高字符串中的 "cm" 后缀String heightStr = fields[3].replace("cm", "").trim();double height = Double.parseDouble(heightStr); // 解析为 doubleAthlete athlete = new Athlete(name, gender, nationality, height,height); athletes.add(athlete);}}// 打印运动员信息for (Athlete athlete : athletes) {System.out.println(athlete); // 确保 Athlete 类有合适的 toString() 方法}} catch (IOException | NumberFormatException e) {e.printStackTrace();// 添加记录日志或通知用户的方法。} finally {if (reader != null) {try {reader.close();} catch (IOException e) {e.printStackTrace();}}}}
}

运行结果如下：

4、集合到文件;

测试代码：

创建一个鲜花类：

package test.com;
public class Flower {private String name;private String color;private int petals;private int quantity;private String origin;// 构造方法public Flower(String name, String color, int petals, int quantity, String origin) {this.name = name;this.color = color;this.petals = petals;this.quantity = quantity;this.origin = origin;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getColor() {return color;}public void setColor(String color) {this.color = color;}public int getPetals() {return petals;}public void setPetals(int petals) {this.petals = petals;}public int getQuantity() {return quantity;}public void setQuantity(int quantity) {this.quantity = quantity;}public String getOrigin() {return origin;}public void setOrigin(String origin) {this.origin = origin;}// 格式化输出方法public String toFormattedString() {return String.format("%s，%s，%d，%d，%s", name, color, petals, quantity, origin);}
}

将集合写入到：E:\\Test\\flowers.txt文本文件中。

package test.com;
import java.io.BufferedWriter;  
import java.io.FileWriter;  
import java.io.IOException;  
import java.util.ArrayList;  
import java.util.List;  
public class FlowerListToFile {  public static void main(String[] args) {  List<Flower> flowers = new ArrayList<>();  flowers.add(new Flower("玫瑰", "红色", 26, 10, "中国"));  flowers.add(new Flower("郁金香", "黄色", 6, 20, "荷兰"));  flowers.add(new Flower("菊花", "白色", 100, 5, "日本"));  // 文件路径  String filePath = "E:\\Test\\flowers.txt";  // 写入文件  try (BufferedWriter writer = new BufferedWriter(new FileWriter(filePath))) {  for (Flower flower : flowers) {  writer.write(flower.toFormattedString());  writer.newLine(); // 换行  }  } catch (IOException e) {  e.printStackTrace();  }  System.out.println("鲜花数据已写入文件：" + filePath);  }  
}

运行结果如下：