Java 在调用getter方法时获取NullPointerException

我有三个班，学生主修，学生服务，学生。Student类包含getter和setters方法，我从StudentMain将Student对象传递给StudentService。代码如下：

StudentMain的代码：

public class StudentMain {
static Student data [] = new Student[4];
static { for (int i = 0; i < data.length; i++) 
    data [i] =new Student();
    data [0] = new Student ("Sekar", new int [] {35, 35, 35}); 
    data [1] = new Student(null,new int[]{11,22,33});
    data [2] = null; 
    data [3] = new Student ("Manoj", null);

}
public static void main(String[] args) {
    // TODO Auto-generated method stub
    StudentService studentService = new StudentService ();
    System.out.println ("Number of Objects with Marks array as null =" + studentService.findNumberOfNullMarks (data));
    System.out.println ("Number of Objects with Name as null="+ studentService.findNumberOfNullNames(data));
    System.out.println ("Number of Objects that are entirely null="+ studentService.findNumberOfNullObjects(data));
    }

public class Student {
private String name;
private int marks[];
public void setName(String name) {
    this.name=name;
}
public String getName() {
    return name;
}
public void setMarks(int [] marks) {
    this.marks=marks;
}
public int[] getMarks() {
    return marks;
}
public Student() {

}
public Student(String name,int[] marks) {
    setName(name);
    setMarks(marks);
}

public class StudentService{
Student[] data;
public int findNumberOfNullMarks(Student data[]) {
    this.data=data;
    int count=0;
    int i=0;
    while(i!=data.length) {
        if(data[i].getMarks()==null)
            count++;
        i++;
    }
    return count;
}
public int findNumberOfNullNames(Student data[]) {
    int count=0;
    int i=0;
    while(i!=data.length) {
        if(data[i].getName()==null)
            count++;
        i++;
    }
    return count;
}
public int findNumberOfNullObjects(Student data[]) {
    int count=0;
    int i=0;
    while(i!=data.length) {
        if(data[i]==null)
            count++;
        i++;
    }
    return count;
}

}

学生服务代码：

public class StudentMain {
static Student data [] = new Student[4];
static { for (int i = 0; i < data.length; i++) 
    data [i] =new Student();
    data [0] = new Student ("Sekar", new int [] {35, 35, 35}); 
    data [1] = new Student(null,new int[]{11,22,33});
    data [2] = null; 
    data [3] = new Student ("Manoj", null);

}
public static void main(String[] args) {
    // TODO Auto-generated method stub
    StudentService studentService = new StudentService ();
    System.out.println ("Number of Objects with Marks array as null =" + studentService.findNumberOfNullMarks (data));
    System.out.println ("Number of Objects with Name as null="+ studentService.findNumberOfNullNames(data));
    System.out.println ("Number of Objects that are entirely null="+ studentService.findNumberOfNullObjects(data));
    }

public class Student {
private String name;
private int marks[];
public void setName(String name) {
    this.name=name;
}
public String getName() {
    return name;
}
public void setMarks(int [] marks) {
    this.marks=marks;
}
public int[] getMarks() {
    return marks;
}
public Student() {

}
public Student(String name,int[] marks) {
    setName(name);
    setMarks(marks);
}

public class StudentService{
Student[] data;
public int findNumberOfNullMarks(Student data[]) {
    this.data=data;
    int count=0;
    int i=0;
    while(i!=data.length) {
        if(data[i].getMarks()==null)
            count++;
        i++;
    }
    return count;
}
public int findNumberOfNullNames(Student data[]) {
    int count=0;
    int i=0;
    while(i!=data.length) {
        if(data[i].getName()==null)
            count++;
        i++;
    }
    return count;
}
public int findNumberOfNullObjects(Student data[]) {
    int count=0;
    int i=0;
    while(i!=data.length) {
        if(data[i]==null)
            count++;
        i++;
    }
    return count;
}

}

我在StudentService类中的

if（data[I].getMarks（）=null）

和

if（data[I].getMarks（）=null）

处遇到异常

data [0] = new Student ("Sekar", new int [] {35, 35, 35}); 
data [1] = new Student(null,new int[]{11,22,33});
data [2] = null; 
data [3] = new Student ("Manoj", null);

对于i=0，数据[0]在对象中有对象和数组标记，所以您不会得到java.lang.NullPointerException

对于i=1，数据[1]具有object，并且在object中具有数组标记，所以您不会得到java.lang.NullPointerException

对于i=2，数据[2]为null，因此您将得到java.lang.NullPointerException

对于i=3，数据[3]具有对象，但数组标记为null，因此您将获得java.lang.NullPointerException

所以您需要确保您应该有对象和数组

对于i=0，数据[0]在对象中有对象和数组标记，所以您不会得到java.lang.NullPointerException

对于i=1，数据[1]具有object，并且在object中具有数组标记，所以您不会得到java.lang.NullPointerException

对于i=2，数据[2]为null，因此您将得到java.lang.NullPointerException

对于i=3，数据[3]具有对象，但数组标记为null，因此您将获得java.lang.NullPointerException

---

因此，您需要确保应该有对象和数组。

data[2]==null数据[2]==null