import java.util.ArrayList;
import java.util.List;
public class arr {
public arr () {
// creat empty list
List<Integer> alpha = new ArrayList<>();
}
public static void main (String []args ) {
arr com1 = new arr();
arr com2= new arr();
//returning false but should be true the two are empty array
com1.equals(com2);
}
}
I am trying to create a class that can build a an empty array but when I am trying to compare the two-object its returning false, but the two have an empty arraylist so it should return true
You are trying to call a missing method called isEmpty()
.
You also need to move the list alpha
as a field for the class, so that it can be accessed by the isEmpty()
method.
To check for equality, just overload the equals()
method.
Also as @Billy mentioned, you should override the hashCode too (so that it'll still work if you use hashSet/hashMap to store the arr class later on in your codes)
import java.util.ArrayList;
import java.util.List;
public class arr {
List<Integer> alpha = new ArrayList<>();
//creates the isEmpty method
boolean isEmpty() {return alpha.isEmpty();}
//check if two arr classes are the same
@Override
public boolean equals(Object obj) {
if (obj == this) return true;
if (obj == null || obj.getClass() != this.getClass())
return false;
arr other = (arr) obj;
//checks if the alpha of this is the same as the alpha in obj
return alpha.equals(other.alpha);
}
//also override the hashCode method so that it'll work correctly for hash containers like hashMap and hashSet.
@Override
public int hashCode(){ return alpha==null?0: alpha.hashCode(); }
public static void main (String []args ) {
arr com1 = new arr();
arr com2= new arr();
//calling the isEmpty() method from the main.
System.out.println("com1 Empty? =" +com1.isEmpty());
//checks if com1 and com2 are equal
System.out.println("com1 same as com2? =" +com1.equals(com2));
}
}
You can use size() method to check Arraylist size. Checkout this for further reference: https://www.geeksforgeeks.org/arraylist-size-method-in-java-with-examples/
Your code is syntactically wrong.
class arr
arr() is a method, so:
Naming still messy, but now at lest you can see it compiling (I hope)
import java.util.ArrayList;
import java.util.List;
public class ArrCreator
{
public List<Integer> createEmptyList()
{
// create empty list
List<Integer> alpha = new ArrayList<>();
return alpha;
}
public static void main(String[] args)
{
ArrCreator creator = new ArrCreator();
List<Integer> com1 = creator.createEmptyList();
List<Integer> com2 = creator.createEmptyList();
System.out.println(com1.equals(com2));
}
}
output: true
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