LinkedHashMap program is giving is not generic; it cannot be parameterized error

Question

I have made a Student class and it in not getting initialized with LinkedHashMap. Giving compile time error :

The type LinkedHashMap is not generic; 
it cannot be parameterized with arguments <Student, Integer>.

CODE :

StudentLinkedMap :

 public class LinkedHashMap {
public static void main(String[] args) {
Map <Student,Integer> students = new LinkedHashMap<Student,Integer>();
Student s1 = new Student(1,2,"Dhwani","Pandya");
Student s2 = new Student(2,2,"Priyam ","Parekh");
Student s3 = new Student (3,2,"Sucheta","Shrivastava");
Student s4 = new Student(3,6,"Nirali","Rokadia");
Student s5 = new Student(2,6,"Kajari","Agrawal");
students.put(s1,2);
students.put(s2,4);
students.put(s3,6);
students.put(s4,5);
students.put(s5,7);
for(Map.Entry lhs:students.entrySet()){
 System.out.println(lhs.getKey()+ " "+ lhs.getValue());
}
}
}

Student Class:

 public class Student {
private int rollno;
private String firstname;
private String lastname;
private int std;
 public Student(int rollno, int std,String firstname, String lastname){
 this.firstname=firstname;
 this.lastname=lastname;
 this.rollno=rollno;
 this.std=std;
 }
@Override
public String toString(){
 return ("\troll no="+ this.rollno + "\tstandard="+ 
 this.std+"\tfirstname="+this.firstname+"\tlastname="+this.lastname);
 }
 }

Answer 1

You have named your class LinkedHashMap so the name shadows java.util.LinkedHashMap. You can either change the name of your class, or use the fully qualified class name.

Map<Student,Integer> students = new java.util.LinkedHashMap<>();

• user8512831: after making the changes gives the error - LinkedHashMap cannot be resolved to a type
• user8512831: But i am getting the same 6 outputs - roll no=2 standard=6 firstname=Kajari lastname=Agrawal 2 roll no=2 standard=6 firstname=Kajari lastname=Agrawal 4 roll no=2 standard=6 firstname=Kajari lastname=Agrawal 6 roll no=2 standard=6 firstname=Kajari lastname=Agrawal 5 roll no=2 standard=6 firstname=Kajari lastname=Agrawal 7
• Elliott Frisch: That is a runtime error, seems like your compiler error is fixed. You are using Student as a key to the Map, but you aren't overriding hashCode... do so (and don't forget to override equals as well).
• user8512831: . why is overriding hashcode and equals so important
• Elliott Frisch: Because a Map (or Set) doesn't allow duplicate keys, so the first thing it does is get the hash of instances to determine where to store it. Once it has that it compares with any values already there, if they're equal it stores the new instance and evicts the old one.