了解 try &捕获和错误处理 [英] Understanding try & catch and error handling
问题描述
import java.util.Scanner;
public class Lab4_5 {
public static void main(String[]args) {
Scanner scan= new Scanner(System.in);
int rows=0;
int rowIndex=0, colIndex=0;
boolean choice1= true;
String y="y";
String n="n";
boolean first = true;
while (choice1==true) {
if (first==true) {
first=false;
System.out.println("Do you want to start(Y/N): ");
} else if (first==false) {
System.out.println("Do you want to continue(Y/N): ");
}
String choice2=scan.next();
if (choice2.equals(y)) {
System.out.println("How many rows/columns(5-21)?");
rows=scan.nextInt();
while (rows<5 || rows>21) {
System.out.println("That is either out of range or not an integer, try again! ");
rows=scan.nextInt();
}
System.out.println("What character?");
String choice3=scan.next();
System.out.println(" ");
for (rowIndex=1; rowIndex<=rows; rowIndex++) {
for (colIndex=1; colIndex<=rows; colIndex++) {
if (rowIndex==1 || rowIndex==rows || colIndex==1 || colIndex==rows) {
System.out.print(choice3);
} else {
System.out.print(" ");
}
}
System.out.println();
}
} else if(choice2.equals(n)) {
choice1 = false;
System.out.println("Thank you. Goodbye.");
} else {
System.out.println("Please either enter Y or N.");
}
}
}//end of main
}
代码打印了我需要它打印的内容,但是当它询问有多少行/列来捕获我是否输入了整数以外的内容时,我还必须在代码中添加一些内容(在下面的部分中).需要一些帮助,我们还没有做任何关于如何捕获异常的事情,我不知道如何开始.
The code prints what I need it to print, but I also have to have something in the code when it asks how many rows/columns to catch whether or not i input something other than an integer(in the part below). need some help, we haven't done anything yet with how to catch exceptions and i don't know how to start.
String choice2=scan.next();
if (choice2.equals(y)) {
System.out.println("How many rows/columns(5-21)?");
rows=scan.nextInt();
while (rows<5 || rows>21) {
System.out.println("That is either out of range or not an integer, try again! ");
rows=scan.nextInt();
}
}
推荐答案
你需要了解 这个请看一下.
You need to understand this please look into it.
基本理解是
try {
//Something that can throw an exception.
} catch (Exception e) {
// To do whatever when the exception is caught.
}
还有一个 finally 块,即使出现错误也会始终执行.它是这样使用的
There is also an finally block which will always be execute even if there is an error. it is used like this
try {
//Something that can throw an exception.
} catch (Exception e) {
// To do whatever when the exception is caught & the returned.
} finally {
// This will always execute if there is an exception or no exception.
}
在您的特定情况下,您可能有以下例外情况(链接).
In your particular case you can have the following exceptions (link).
InputMismatchException - 如果下一个标记与 Integer 正则表达式不匹配,或者超出范围NoSuchElementException - 如果输入已用尽IllegalStateException - 如果此扫描器已关闭
InputMismatchException - if the next token does not match the Integer regular expression, or is out of range NoSuchElementException - if input is exhausted IllegalStateException - if this scanner is closed
所以你需要捕捉像
try {
rows=scan.nextInt();
} catch (InputMismatchException e) {
// When the InputMismatchException is caught.
System.out.println("The next token does not match the Integer regular expression, or is out of range");
} catch (NoSuchElementException e) {
// When the NoSuchElementException is caught.
System.out.println("Input is exhausted");
} catch (IllegalStateException e) {
// When the IllegalStateException is caught.
System.out.println("Scanner is close");
}
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