**這是我創建改變字段在Java
class Student{
private String name;
private float avGrade;
private float outstandingGrade = 82.0f;
public Student() { }
public Student(String Name, float avg) {
name = Name;
avGrade = avg;
}
public String getName() {
return name;
}
public void setName(String Name) {
name = Name;
}
}
類的一部分,這是主要的並且在它的另一方法:
public static void main(String[] args) {
Student[][] school = CreateStudentMat();
school[0][0].setName("Student");
}
public static Student[][] CreateStudentMat(){
Scanner input = new Scanner(System.in);
System.out.println("Please enter number of classes in school: ");
int NumClasses = input.nextInt();
Student[][] matrix = new Student[NumClasses][];
for(int i = 0; i<matrix.length; i++){
System.out.println("Please enter number of students in class " +(i+1));
matrix[i] = new Student[input.nextInt()];
}
return matrix;
}
當我試圖改變對象名稱[0] [0] 與學校[0] [0] .setName(「學生」);
我得到一個錯誤
異常線程 「main」 顯示java.lang.NullPointerException 在Homework3.main(Homework3.java:13)
我做錯了什麼嗎?