polymorphisme et héritage en java
Bonsoir,
J'ai un problème que je n'arrive pas à résoudre en fait j'ai une classe personne et deux sous classes fils teacher et Student. une 3 ème classe université qui contient un tableau qui contient 3 teachers et 3 student puis je veux afficher les détails du tableau
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| package test;
public abstract class Person {
protected String name;
protected int age;
public Person(String n, int a){
name=n;
age=a;
}
public String getName(){
return name;
}
public int getAge(){
return age;
}
public void setName(String n){
name=n;
}
public void setAge(int a){
age=a;
}
public abstract void print();
} |
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| package test;
public class Teacher extends Person {
private float salary;
public Teacher(String n, int a, float s){
super(n,a);
salary=s;
}
public float getSalary(){
return salary;
}
public void setSalary(float s){
salary=s;
}
public void print(){
name=getName();
age=getAge();
System.out.println("The name of Teacher is "+name+"\n"+" the age of the teacher is "+ age+"\n"+"The salary of the teacher is "+salary);
}
} |
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| package test;
public class Student extends Person {
private int id;
public Student(String name,int age, int id){
super(name,age);
this.id=id;
}
public int getId(){
return id;
}
public void setId(int i){
id=i;
}
public void print(){
System.out.println("The name od the student is "+name+"\n"+"The age of the student is "+age+"\n"+"The id of the student is "+id);
}
} |
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| public class University {
Person tab[];
int size_tab;
int n=0;
public University(int size, int x){
size_tab=size;
n=x;
tab=new Person[size_tab];
}
public int addPerson(Person p){
System.out.println("n= "+n);
tab[n].name=p.name;
tab[n].age=p.age;
System.out.println("Person "+ tab[n]);
n++;
return n;
}
public void PrintAll(){
for (int i=0;i<n;i++){
System.out.println(tab[i]);
}
}
} |
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| package test;
public class Principal {
public static void main(String []args){
Teacher t1=new Teacher("Boutheina",32,9000);
Teacher t2=new Teacher("Abir",29,3500);
Teacher t3=new Teacher ("Asma",25,5000);
Student s1=new Student("Aicha",20,12345);
Student s2=new Student("Meriem",21,45678);
Student s3=new Student ("Zeineb",19,78912);
University u=new University(7,6);
u.addPerson(s3);
u.addPerson(s2);
u.addPerson(s1);
u.addPerson(t3);
u.addPerson(t2);
u.addPerson(t1);
u.PrintAll();
}
} |
cet erreur est affiché:
Exception in thread "main" java.lang.NullPointerException
at test.University.addPerson(University.java:15)
at test.Principal.main(Principal.java:12)
