我在一个名为Bus的类中有一个方法（public void AddBusses）。在方法中有一些int变量来跟踪一些ArrayList的大小。我希望能够在我的主类中使用arrayList的大小。
我尝试在类总线中声明int变量，但这只是使它们都为0，并且不会在方法中给予它们的值。
然后，我尝试使用get方法将它们获取到主类，但结果相同，返回0。
上面讨论的尝试位于Bus类中并被注解掉。
// public int b1;
// public int b2;
// public int b3;
// public int b4;
// public int getB1(){
// return b1;
// }
// public int getB2(){
// return b2;
// }
// public int getB3(){
// return b3;
// }下面是主类中的相关代码：
import java.io.*;
import java.util.*;//Includes ArrayList
public class Bussin
{
public static void main (String []args)
{
//Instantiate 3 ArrayLists
//ArrayList<Student> StudentList = new ArrayList<Student>();
List<Student> StudentList = Collections.synchronizedList(new ArrayList<Student>());
//ArrayList<Bus> Bus = new ArrayList<Bus> ();
List<Bus> BusList = Collections.synchronizedList(new ArrayList<Bus>());
List<Bus2> BusList2 = Collections.synchronizedList(new ArrayList<Bus2>());
//ArrayList<BusStop> BusStop = new ArrayList<BusStop>();
List<BusStop> BusStopList = Collections.synchronizedList(new ArrayList<BusStop>());
File myFile_1_5 = null;
FileWriter myWriter_1_5 = null;
Scanner myReader_1_5 = null;
//1_5
try {
myFile_1_5 = new File("D:\\11th Grade Portfolio\\AP Computer Science A\\ArrayListSizes.txt");
if (myFile_1_5.createNewFile())
{
System.out.println("File created: " + myFile_1_5.getName());
} else {
System.out.println("File already exists.");
myReader_1_5 = new Scanner(myFile_1_5);
int ReadStudentListSize_1_5 = myReader_1_5.nextInt();
int ReadBusListSize_1_5 = myReader_1_5.nextInt();
int ReadBusStopListSize_1_5 = myReader_1_5.nextInt();
System.out.println(ReadStudentListSize_1_5);
System.out.println(ReadBusListSize_1_5);
System.out.println(ReadBusStopListSize_1_5);
myReader_1_5.close();
}
} catch (IOException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
case 2:
Scanner Reader2 = new Scanner(System.in);
int R2 = 0;
while(R2 != -1)
{
System.out.println("\nBusses");
System.out.println("1. Add Busses\n2. Remove Busses\n3. Move Busses\n4. View Busses\n5. View Students\n6. See all Busses");
System.out.println("\n Enter 1-3 to make a selection, or -1 to quit:");
R2 = Reader2.nextInt();
System.out.println("__________________________________________________________________\n");
Bus b = new Bus (BusList);
switch (R2)
{
case -1:
System.out.println("Returning to main menu...");
break;
case 1:
b.AddBusses(StudentList, BusList2, BusStopList);
break;
case 2:
b.RemoveBusses();
break;
case 3:
b.MoveBusses();
break;
case 4:
b.ViewBusses();
break;
case 5:
b.ViewStudents();
break;
case 6:
// b.SeeAllBusses();
System.out.println("______________");
System.out.println("See all Busses");
// Test int StudentListSize = b.b5;
// with int BusListSize = b.b6;
// b5,6,7. int BusStopListSize = b.b7;
// This int StudentListSize = b.getB1();
// was the int BusListSize = b.getB1();
// second attempt. int BusStopListSize = b.getB3();
// This int StudentListSize = b.b1;
// was the int BusListSize = b.b2;
// first attempt. int BusStopListSize = b.b3;
try {
myWriter_1_5 = new FileWriter("D:\\11th Grade Portfolio\\AP Computer Science A\\ArrayListSizes.txt");
myWriter_1_5.write(StudentListSize + "\n");//+ " " + BusListSize + " " + BusStopListSize);
myWriter_1_5.write(BusListSize + "\n");
myWriter_1_5.write(BusStopListSize + "\n");
System.out.println("Successfully wrote to the file.");
myWriter_1_5.close();
} catch (IOException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
//Read from the file
try {
myReader_1_5 = new Scanner(myFile_1_5);
while (myReader_1_5.hasNextLine())
{
String data1_5 = myReader_1_5.nextLine();
System.out.println(data1_5);
}
myReader_1_5.close();
} catch (IOException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
try {
myWriter_2 = new FileWriter("D:\\11th Grade Portfolio\\AP Computer Science A\\Busses.txt");
ListIterator<Student> l = StudentList.listIterator();
while(l.hasNext())
{
myWriter_2.write(l.next().toString().toUpperCase()) ;
}
myWriter_2.write("\n");
ListIterator<Bus2> m = BusList2.listIterator();
while(m.hasNext())
{
myWriter_2.write(m.next().toString().toUpperCase());
}
myWriter_2.write("\n");
ListIterator<BusStop> n = BusStopList.listIterator();
while(n.hasNext())
{
myWriter_2.write(n.next().toString().toUpperCase());
}
System.out.println("Successfully wrote to the file.");
myWriter_2.close();
} catch (IOException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
//Read from the file
try {
myReader_2 = new Scanner(myFile_2);
while (myReader_2.hasNextLine())
{
String data = myReader_2.nextLine();
System.out.println(data);
}
myReader_2.close();
} catch (IOException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
break;
}
}我忘了说主类中的大部分代码是嵌套菜单的一部分，所以我没有包括大菜单的开始，但你可以在上面的代码中看到一个嵌套菜单。
下面是总线类的相关代码：（对不起，我很困惑我自己：）
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.io.*;
public class Bus
{
//public String Bus;
public List<Bus2> Bus_B;
public List<Student> StudentList_B;
public List<BusStop> BusStopList_B;
//public Bus(List<Student> StudentList2, String Bus2, List<BusStop> BusStopList2)
public Bus(List<Student> StudentList2, List<Bus2> BusList3, List<BusStop> BusStopList2)
{
StudentList_B = StudentList2;
//Bus = Bus2;
Bus_B = BusList3;
BusStopList_B = BusStopList2;
}
//Stuff for all methods to use
static Scanner Reader_B = new Scanner(System.in);
private List<Bus> BusList;
Bus(List<Bus> BusList)
{
this.BusList = BusList;
}
// public int b1;
// public int b2;
// public int b3;
// public int b4;
// public int getB1()
// {
// return b1;
//
// }
// public int getB2()
// {
// return b2;
//
// }
// public int getB3()
// {
// return b3;
// }
public int b5 = 69; // b5,6,& 7 were just tests to access the ints- these worked and
public int b6 = 420; // was able to access the value, but only b/c I initialized
public int b7 = 911; // the method.
public void AddBusses (List<Student> StudentList2, List<Bus2> BusList3, List<BusStop> BusStopList2)
{
String Bus2;
String Name2;
String BusStop2;
int StudentCount;
int BusStopCount;
System.out.println("__________");
System.out.println("Add Busses");
System.out.println("Enter the number of the new Bus:");
Bus2 = Reader_B.nextLine();
Bus2 NewBus_B = new Bus2 (Bus2);
BusList3.add(NewBus_B);
int b2 = BusList3.size();
System.out.println("The size of the array is " + b2 + ". The bus number is " + NewBus_B.Bus + ".");
System.out.println("How many students ride Bus " + Bus2 + "?");
StudentCount = Reader_B.nextInt();
System.out.println("Enter the names of the " + StudentCount + " Students that ride Bus " + Bus2 + ".");
Name2 = Reader_B.nextLine();
for (int i = 0; i < StudentCount; i++)
{
System.out.println("Student Name:");
Name2 = Reader_B.nextLine();
Student NewStudent_B = new Student(Name2, Bus2);
StudentList2.add(NewStudent_B);
int b1 = StudentList2.size();
System.out.println("the size of the array is " + b1 + ". The student's name is " + NewStudent_B.Name + " and their bus number is " + NewStudent_B.BusNumber + ".");
}
System.out.println("\nHow many Bus Stops does " + Bus2 + " stop at?");
BusStopCount = Reader_B.nextInt();
System.out.println("Enter the names of the " + BusStopCount + " Bus Stops that Bus " + Bus2 + " stops at.");
BusStop2 = Reader_B.nextLine();
for (int j = 0; j < BusStopCount; j++)
{
System.out.println("Bus Stop Name:");
BusStop2 = Reader_B.nextLine();
BusStop NewBusStop_B = new BusStop(BusStop2, Bus2);
BusStopList2.add(NewBusStop_B);
int b3 = BusStopList2.size();
System.out.println("The size of the array is " + b3 + ". The name of the new Bus Stop is " + NewBusStop_B.BusStop + ".");
}
Bus NewBus = new Bus(StudentList2, BusList3, BusStopList2);
BusList.add(NewBus);
int b4 = BusList.size();
System.out.println("The size of the array is " + b4 + ".");
}
2条答案
按热度按时间cdmah0mi1#
从我在代码中看到的情况来看，你从来没有在一个方法中为b1、2、3或4 accept赋值，如果你运行AddBusses（）方法，b1应该是一个有效值。
c3frrgcw2#
我可以解决我的问题！
在Bus类中，我在方法外部将int变量声明为 public static int，然后从方法中删除声明语句。
在Main类中，我通过调用类访问变量，然后访问变量。
下面是新旧代码的示例：
相关主类代码：之前（2种不同方式）：
之后：
相关总线类代码：之前（2次不同尝试）：
内部方法：
之后：
内部方法：