无限循环被卡住，java中的代码出现问题
无限循环被卡住，java中的代码出现问题
提问于 2020-03-13 23:55:43
手头的任务是创建一个血液传输管理器应用程序，它可以有效地选择输血的捐赠者。
当应用程序启动时，它应该尝试打开两个文件：“donors.txt”和“recipients.txt”。如果其中一个文件丢失，程序应该通知问题并退出。这两个文件的格式都应该是:每一行都应该包含一个人的全名和他们的血型，用分号分隔。程序应该首先读取donors.txt，将每一行拆分为姓名和血型，并将结果数组作为新元素存储在捐赠者数组列表中。它还应该将列表打印在屏幕上，并检查每个人的血型是否有效。如果发现无效的血型，则不应将该条目添加到数组列表中，并且应通知用户哪个条目有问题。然后，应以类似的方式读取、处理和存储收件人(在收件人数组中)这是任务的一部分
这是我之前的代码，在更多地更新它以接近任务结束时，我发现代码停止了工作，我对它进行了调试，发现它陷入了无限循环，不确定如何修复它，或者是否有任何其他方法可以重写它以使其工作，可能不使用while循环
package java_assigment_4;
import java.io.*;
import java.util.*;
public class java_assigment_4 {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner file_donors;
Scanner file_recp;
ArrayList list_donors = new ArrayList();
ArrayList list_recp = new ArrayList();
String blood_type = "o- o+ a- a+ b- b+ ab- ab+";
try
{
file_donors = new Scanner(new FileReader("donors.text"));
while (file_donors.hasNextLine())
{
list_donors.add(file_donors.nextLine()); // store donors names & blood type in array list
}//end while
file_donors.close();
}//end try
catch (FileNotFoundException e)
{
System.out.println("Error: " + e.getMessage());
}//end catch
try
{
file_recp = new Scanner(new FileReader("recipients.text"));
while (file_recp.hasNextLine())
{
list_recp.add(file_recp.nextLine()); // store recipents names & blood type in array list
}//end while
file_recp.close();
}//end try
catch (FileNotFoundException e)
{
System.out.println("Error: " + e.getMessage());
}//end catch
System.out.println("donors " + list_donors);
System.out.println("\n");
System.out.println("recipents " + list_recp);
// for (int i=0;i<list_donors.size();i++) {
// list_donors.contains(";"); // need a substring to store type after ;
}
}
}下面的代码是最新的代码，也是不起作用的代码
public class java_assigment_4 {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner file_donors;
Scanner file_recp;
ArrayList<String> list_donors = new ArrayList<String>();
ArrayList<String> list_recp = new ArrayList<String>();
String [] blood_type = {"o-","o+","a-","a+","b-","b+","ab-","ab+"};
try
{
file_donors = new Scanner(new FileReader("donors.txt"));
while (file_donors.hasNextLine())
{
for (int i=0;i<list_donors.size();i++) {
String donor=list_donors.get(i);
String type =donor.substring((donor.indexOf(";") + 1)); // look for ; and stores info after witch is the blood type into a substring so i can use for checking if vaild
type=type.trim();
for (int z=0;z<blood_type.length;z++) {
if (type.equals(blood_type [z])) { compares the two lists
list_donors.add(file_donors.nextLine()); // store donors names & blood if vaild type in array list
}
else {
System.out.println( "this person with blood;" + type + " is not valid ");
}
}
}
}
file_donors.close();
}
catch (FileNotFoundException e)
{
System.out.println("Error: " + e.getMessage());
}
System.out.println("donors " + list_donors);
try
{
file_recp = new Scanner(new FileReader("recipients.txt"));
while (file_recp.hasNextLine())
{
for (int i=0;i<list_recp.size();i++) {
String recp=list_recp.get(i);
String type =recp.substring((recp.indexOf(";") + 1));
type=type.trim();
for (int z=0;z<blood_type.length;z++) {
if (type.equals(blood_type [z])) { // compares the two lists
list_recp.add(file_recp.nextLine()); // store recp names & blood type if vaild in array list
}
else {
System.out.println( "this person with blood ;" + type + " is not valid ");
}
}
}
}
file_recp.close();
}
catch (FileNotFoundException e)
{
System.out.println("Error: " + e.getMessage());
}
// System.out.println("donors " + list_donors);
// System.out.println("\n");
// System.out.println("recipents " + list_recp);
}
}回答 1
Stack Overflow用户
发布于 2020-03-14 00:36:56
list_donors.size()将始终返回0，因为list_donors在开始时为空
因此代码永远不会调用file_donors.nextLine()
而file_donors.hasNextLine()将永远是真的
public class java_assigment_4 {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner file_donors;
Scanner file_recp;
ArrayList<String> list_donors = new ArrayList<String>();
ArrayList<String> list_recp = new ArrayList<String>();
String [] blood_type = {"o-","o+","a-","a+","b-","b+","ab-","ab+"};
try
{
file_donors = new Scanner(new FileReader("donors.txt"));
// file_donors.hasNextLine() always true in your code
while (file_donors.hasNextLine())
{
// list_donors.size() will return 0, cause the list_donors is empty when it begins
// so the code never enter this for and never call file_donors.nextLine()
for (int i=0;i<list_donors.size();i++) {
...
}
}你可以像这样做来避免这种情况
while (file_donors.hasNextLine())
{
string current_line = file_donors.hasNextLine();使用一些代码进行更新以提供帮助
import java.io.*;
import java.util.*;
public class Blood
{
public static void main(String[] args)
{
ArrayList<String> list_donors = new ArrayList<String>();
ArrayList<String> list_recp = new ArrayList<String>();
System.out.println("Starting!");
copyFromFile("/home/mitz/stackoverflow/java/Donors.txt", list_donors);
System.out.println("imported "+ list_donors.size() + " registers");
copyFromFile("/home/mitz/stackoverflow/java/Receptors.txt", list_recp);
System.out.println("imported "+ list_recp.size() + " registers");
System.out.println("Finished!");
}
public static void copyFromFile(String filename, ArrayList<String> listDestiny)
{
Scanner fileScanner;
FileReader fileReader;
try
{
fileReader = new FileReader(filename);
fileScanner = new Scanner(fileReader);
while (fileScanner.hasNextLine())
{
String currentLine = fileScanner.nextLine();
String type = currentLine.substring((currentLine.indexOf(";") + 1));
if(isValidBloodType(type))
{
listDestiny.add(currentLine);
System.out.println("Imported: " + currentLine);
}else{
System.out.println("Invalid blood type!! Alien detected with blood type: " + type);
}
}
fileScanner.close();
}
catch (FileNotFoundException e)
{
System.out.println("Arquivo não encontrado");
}
}
public static Boolean isValidBloodType(String type)
{
String[] blood_type = {"o-", "o+", "a-", "a+", "b-", "b+", "ab-", "ab+"};
return Arrays.asList(blood_type).contains(type);
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/60673593
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