How to separate different values in 2-d array

问题

The array has objects from different subclasses. How can I print the objects according to there subclasses?

I used scanner to read student (Graduate and Undergraduate) objects and put into an array.

I need to use inheritance and toString methods to get the results.

Original data in txt file:

G Steve 23 Biology

U Julia 19 Music Flute, year: Sophomore

G David 25 Math

I was able to read and print the objects but only in original order:

Graduate Name:Steve, Age: 23, Major: Biology

Undergraduate Name: Julia, Age: 19, Major: Music, year: Sophomore

Graduate Name: Dvid, Age: 25, Major: Math

Below is the method I used in tester file:

ArrayList<Student> studentList = new ArrayList<>();
Student s = new Undergraduate(type,name,age,major,year);
studentList.add(s);
Student s = new Graduate(type,name,age, major);
studentList.add(s);

for (Student d:studentList) {
System.out.println(d.toString());
}

=== Expected result:===

Number of Undergraduate Student: 1

Name: Julia, Age: 19, Major: Music, year: Sophomore

Number of Graduate Student: 2

Name:Steve, Age: 23, Major: Biology

Name:Dvid, Age: 25, Major: Math

===

This is my first question here. I am not familiar with the system. I tried to make my question easier to read. Sorry if it looks messy.

回答1:

You can use instanceof to separate the different types of objects. ex.

if (s instanceof Undergraduate){
   Undergraduate u = (Undergraduate) s;
}

You can iterate your list and count your objets using instanceof. You can do the check above during the input too.

回答2:

The simplest way of doing this is to create two separate ArrayLists: One for Undergraduate students and one for Graduate students:

ArrayList<Student> undGrdStudentList = new ArrayList<>();
ArrayList<Student> grdStudentList = new ArrayList<>();
if ("U".equals(type)){
  Student s = new Undergraduate(type,name,major);
  undGrdStudentList.add(s);
}else{
  Student s = new Graduate(type,name,major);
  grdStudentList .add(s);
}

System.out.println("Number of Undergraduate Students: " + undGrdStudentList.size());
for (Student d:undGrdStudentList) {
  System.out.println(d.toString());
}

System.out.println("Number of Graduate Students: " + grdStudentList .size());
for (Student d:grdStudentList ) {
  System.out.println(d.toString());
}

Something like that

回答3:

Triple<String,Integer,String> student;
List<Triple<String,Integer,String>> UstudentList = new ArrayList<>();
student = new MutableTriple<>("jin",23,"biology");
UstudentList.add(student);
List<Triple<String,Integer,String>> GstudentList = new ArrayList<>();
student = new MutableTriple<>("amol",23,"music");
GstudentList.add(student);

Triple class is from org.apache.commons.lang3.tuple.Triple

for your expected result

 System.out.println("No. of Undergraduate: "+UstudentList.size())
for (Triple<String,Integer,String> stud: UstudentList) {
            System.out.println(stud.getLeft()+stud.getMiddle()+stud.getRight());
        }
 System.out.println("No. of Graduate: "+GstudentList.size())
for (Triple<String,Integer,String> stud: GstudentList) {
            System.out.println(stud.getLeft()+stud.getMiddle()+stud.getRight());
        }

来源：https://stackoverflow.com/questions/58371462/how-to-separate-different-values-in-2-d-array

标签

java

arrays

multidimensional-array