public class IOException{
// 获取系统默认的行分隔符
private static final String LINE_SEPARATOR = System.getProperty("line.separator");
public static void main(String[] args){
try{
FileWriter fw = new FileWriter("test.md");
fw.write("abc"+LINE_SEPARATOR+"haha");
} catch (IOException){
System.out.println(e.toString());
} finally{
fw.close(); // 此时, fw 是局部变量, 只在 try 内部有效, 此时 fw 属于未定义变量
}
}
}
// 改进第一步:
public class IOException{
// 获取系统默认的行分隔符
private static final String LINE_SEPARATOR = System.getProperty("line.separator");
public static void main(String[] args){
FileWriter fw = null; // 创建流对象
try{
// 流对象初始化
fw = new FileWriter("k:\\test.md");
fw.write("abc"+LINE_SEPARATOR+"haha");
} catch (IOException){
System.out.println(e.toString());
} finally{
try{
fw.close();// 此处有可能出现关闭失败的异常, 所以也许要 try catch
} catch (IOException e){
throw new RuntimeException("关闭失败");
}
}
}
}
// 运行上述程序:
public class IOException{
// 获取系统默认的行分隔符
private static final String LINE_SEPARATOR = System.getProperty("line.separator");
public static void main(String[] args){
FileWriter fw = null;
try{
// 流对象初始化
fw = new FileWriter("k:\\test.md"); // 此处出现异常: FileNotFoundException
// 该异常是 IOException 的子类
fw.write("abc"+LINE_SEPARATOR+"haha");
} catch (IOException){
System.out.println(e.toString);
} finally{
try{
fw.close(); // 由于文件没有创建成功, 因此此处抛出 NUllPointerException
} catch (IOException e){
throw new RuntimeException("关闭失败");
}
}
}
}
// 改进第二步:
public class IOException{
// 获取系统默认的行分隔符
private static final String LINE_SEPARATOR = System.getProperty("line.separator");
public static void main(String[] args){
FileWriter fw = null;
try{
// 流对象初始化
fw = new FileWriter("k:\\test.md"); // 此处出现异常: FileNotFoundException
// 该异常是 IOException 的子类
fw.write("abc"+LINE_SEPARATOR+"haha");
} catch (IOException){
System.out.println(e.toString);
} finally{
if(fw != null) // 增加一条判断语句
try{
fw.close();
} catch (IOException e){
throw new RuntimeException("关闭失败");
}
}
}
}
参考资料: