我有一个简单的'家庭作业',但我发现输入流的关闭有点问题。 简单地说,我必须用Java创建一个联系人'列表'应用程序,只是以正确的方式使用多态。所以我有一个类Contact和一个子类Private(联系人)。在这两个类中都有一个修改方法来更改变量的值。
public void modify() throws IOException {
System.out.println("Previously name: " + name);
System.out.println("Insert new name");
try(InputStreamReader ir = new InputStreamReader(System.in);
BufferedReader in = new BufferedReader(ir) ) {
name= in.readLine();
System.out.println("You've changed the name to: "+ name);
System.out.println("Previously surname: " + surname);
System.out.println("Insert new surname");
surname= in.readLine();
System.out.println("You've changed the surname to: "+ surname);
System.out.println("Previously e-mail: " + email);
System.out.println("Insert new e-mail");
email = in.readLine();
System.out.println("You've changed the e-mail to: "+ email); }
}
这是不会产生问题的Contact方法
@Override
public void modify() throws IOException {
super.modifica();
System.out.println("Numero di cellulare precedente: " + cell);
System.out.println("Inserire nuovo numero");
try (InputStreamReader ir = new InputStreamReader(System.in);
BufferedReader in = new BufferedReader(ir)) {
cell = in.readLine();
System.out.println("Hai cambiato il numero in: "+ cell);
System.out.println("Contatto skype precedente: " + skype);
System.out.println("Inserire nuovo contatto");
skype = in.readLine();
System.out.println("Hai cambiato il contatto in: "+ skype);
}
}
相反,这是Private中方法的覆盖。 在main中,我创建了一个Private对象,我调用了modify方法。我可以毫无问题地插入名称,姓氏和电子邮件,然后该方法抛出IO异常,因为流已关闭。 我无法理解为什么会遇到这种问题。我认为通过尝试使用第一个代码中的资源来关闭流,但是然后通过另一个尝试使用资源在第二个代码中打开它。可能我的想法中的某些内容是错误的。
答案 0 :(得分:0)
你的问题确实是由于关闭new InputStreamReader(System.in)
的try-with-resource语句,在场景后面关闭了基础输入流System.in
(in
是{{} 1}} public static
}的字段,使得System
方法modify
已经关闭,然后无法再读取,这就是您获得此异常的原因。
答案 1 :(得分:0)
如果您使用try-with-resources
打包System.in
,您仍然可以使用CloseShieldInputStream
。
我还建议使用Scanner
代替InputStreamReader
和BufferedReader
,因为它很简单:
import java.util.Scanner;
import org.apache.commons.io.input.CloseShieldInputStream;
public class Contact {
protected String name;
protected String surname;
protected String email;
public void modify() throws IOException {
System.out.println("Previously name: " + name);
System.out.println("Insert new name");
try (Scanner sc = new Scanner(new CloseShieldInputStream(System.in))) {
name = sc.nextLine();
System.out.println("You've changed the name to: " + name);
System.out.println("Previously surname: " + surname);
System.out.println("Insert new surname");
surname = sc.nextLine();
System.out.println("You've changed the surname to: " + surname);
System.out.println("Previously e-mail: " + email);
System.out.println("Insert new e-mail");
email = sc.nextLine();
System.out.println("You've changed the e-mail to: " + email);
}
}
}
public class Private extends Contact {
private String cell;
private String skype;
@Override
public void modify() throws IOException {
super.modify();
System.out.println("Numero di cellulare precedente: " + cell);
System.out.println("Inserire nuovo numero");
try (Scanner sc = new Scanner(new CloseShieldInputStream(System.in))) {
cell = sc.nextLine();
System.out.println("Hai cambiato il numero in: " + cell);
System.out.println("Contatto skype precedente: " + skype);
System.out.println("Inserire nuovo contatto");
skype = sc.nextLine();
System.out.println("Hai cambiato il contatto in: " + skype);
}
}
}