Casting

[Ayoub Limouni]

public List<Category> listAll() {



return super.listAll(); <------- returns BaseDao list;

}

the error :The return type is incompatible with BaseDao.listAll();

and i've to return list of Category .

[Campbell Ritchie]

And what is the return type of the superclass' method? Remember a List<Foo> is not a subtype of List<Bar> even if class Foo extends Bar.

[Ayoub Limouni]

this is the super class returns list of Base Model

public List<BaseModel> listAll(

[Ayoub Limouni]

Type mismatch: cannot convert from List<BaseModel> to List<Category> how to do it ?

[Campbell Ritchie]

In which case List<Category> is not a subtype of List<BaseModel> You might get away with returning List<? extends BaseModel>, or if might be better to use polymorphism and stick with List<BasModel>. I am not sure which is better.

[Ayoub Limouni]

package com.news.model;

public class BaseModel {

private Integer id;
private String name;

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public BaseModel() {

}

public BaseModel(Integer id) {
this.id = id;
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String toString() {
return "BaseModel [id=" + id + "]";
}

}
----------------------
package com.news.model;

public class Category extends BaseModel {


}

[Lakshan Dissanayake]

in your Example BaseModel is the super class.
Category is the sub class.
so

Category category = new BaseModel(); //is not allowed.

in your example you've assigned instance of a super class in to a sub class reference.

Hope this helps.
Supun

[Jesper de Jong]

The method listAll in your class returns a List<Category>.

The method listAll in the superclass of your class returns a List<BaseModel>.

Your listAll method is overriding the listAll method in the superclass, but the return type is different: List<Category> instead of List<BaseModel>.

That is a problem, becuase the return types are not compatible. In other words, a List<Category> is not a List<BaseModel>, so you cannot make your overridden method return a List<Category>. Note that even though Category extends BaseModel, a List<Category> does not extend List<BaseModel>.

Ways to solve this:

1. Make the listAll method in your superclass return List<? extends BaseModel> instead of List<BaseModel>.

2. Make the listAll method in your subclass return List<BaseModel> instead of List<Category>.