Java 将ArrayList转换为2D数组-返回ArrayOutOfBounds

我需要创建一个学生列表，并将其转换为座位表（特定长度和宽度的2d数组）。这是我的密码：

public class SeatingChart {
  Student seats[][];
  public SeatingChart(List <Student> studentList, int rows, int cols) {
    seats = new Student[rows][cols];
    for (int i = 0; i < cols; i++) { //Assigns Students in Column by Row order
        for (int j = 0; j < rows; j++) {
            if (i*rows+j > studentList.size() - 1) {
                seats[i][j] = null; //Occupies remaining `seats` with null
            }
            seats[i][j] = studentList.get(i*rows+j); //Finds an error with this line
        }
    }
}

public class Tester {
  public static void main (String[] args) {
    List <Student> classroom = new ArrayList<Student>();
    classroom.add(new Student("Anna", 3));
    SeatingChart sc = new SeatingChart(classroom, 2, 2); //Finds an error with this line
  }
}

public class Student {
  //assigns Name and number of absences for each student
}

公共类座位表{
学生座位[]；
公共座位表（列出学生名单、整数行、整数列）{
座位=新生[排][列]；
对于（int i=0；istudentList.size（）-1）{
seats[i][j]=null；//用null占据剩余的'seats'
}
seats[i][j]=studentList.get（i*rows+j）；//查找此行的错误
}
}
}
公共类测试员{
公共静态void main（字符串[]args）{
列表教室=新建ArrayList（）；
增加（新生（“安娜”，3））；
SeatingChart sc=新的座位图（教室，2，2）；//发现此行有错误
}
}
公立班学生{
//指定每个学生的姓名和缺勤次数
}

这将返回：

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 1, Size: 1
    at java.util.ArrayList.rangeCheck(ArrayList.java:657)
    at java.util.ArrayList.get(ArrayList.java:433)
    at stud2.SeatingChart.<init>(SeatingChart.java:14)
    at stud2.SeatingChartTester.main(SeatingChartTester.java:12)

线程“main”java.lang.IndexOutOfBoundsException中的异常：索引：1，大小：1 位于java.util.ArrayList.rangeCheck（ArrayList.java:657） 获取（ArrayList.java:433） 在stud2.SeatingChart.（SeatingChart.java:14） 在stud2.SeatingChartTester.main（SeatingChartTester.java:12）

---

但是，作为ArrayList类（rangeCheck和get）一部分的错误当我在

教室中再增加两个学生时，错误就消失了。为什么错误被解决了，为什么最后两个错误仍然存在？我已经仔细检查了代码背后的逻辑，并用与ArrayList大小相同的1D数组替换了2D数组，但我得到了相同的错误。
在这里我可以看到问题

  List <Student> classroom = new ArrayList<Student>();
classroom.add(new Student("Anna", 3)); //so size of class room is 1

现在注意

 for (int i = 0; i < cols; i++) { 
    for (int j = 0; j < rows; j++) { // the first iteration in this loop will go fine
        if (i*rows+j > studentList.size() - 1) {
            seats[i][j] = null;
        }
        seats[i][j] = studentList.get(i*rows+j);
 /* but when j is one and i is 0 this expression resolves to i*rows + j == 0*2 + 1 = 1
   means you're saying studentList.get(1) , but list has only one student which is at 
   index 0 , that  
   is why you're getting java.lang.IndexOutOfBoundsException: Index: 1, Size: 1 cuz 
   index 
   is 1 in the get(1) and size is also 1 means noting at index 1.*/
    }
}

for（inti=0；istudentList.size（）-1）{
席位[i][j]=零；
}
seats[i][j]=studentList.get（i*rows+j）；
/*但是当j为1，i为0时，这个表达式解析为i*rows+j==0*2+1=1
意思是你们说的是studentList.get（1），但列表中只有一个学生在
索引0，即
这就是您获取java.lang.IndexOutOfBoundsException的原因：索引：1，大小：1 cuz
指数
get（1）中的值为1，size也为1表示在索引1处注释*/
}
}
@maio290我觉得我用SeatingChart中的if语句检查了ArrayList上存在越界的情况。我发现您需要的只是一个else语句。但是，它现在导致了一个nullPointerException，我找到了它的原因。谢谢！
 for (int i = 0; i < cols; i++) { 
    for (int j = 0; j < rows; j++) { // the first iteration in this loop will go fine
        if (i*rows+j > studentList.size() - 1) {
            seats[i][j] = null;
        }
        seats[i][j] = studentList.get(i*rows+j);
 /* but when j is one and i is 0 this expression resolves to i*rows + j == 0*2 + 1 = 1
   means you're saying studentList.get(1) , but list has only one student which is at 
   index 0 , that  
   is why you're getting java.lang.IndexOutOfBoundsException: Index: 1, Size: 1 cuz 
   index 
   is 1 in the get(1) and size is also 1 means noting at index 1.*/
    }
}