Given the following interface for a list, comment on it from the perspective of an ADT. Consider what is in there and what is missing, what is right and what is wrong. Solution Note Points of Interface: Interface provides the declaration of abstract methods that needs to be implemented in the class by which the interface is implementing. Interface does not have a construcor.It contains the abstract method declaration and static constants. ------------------------------------------------------------------------------------------------------------------------------------------ //Comments are provide which is valid and invalid methods public interface ArrayList { //It is not valid since the class implementing the interface will have to implement only methods //not class constructor //Invalid declaration // public ArrayList(void) { List = 0 }; //constructor - initializes list to be empty //Invalid abstract method since the return type of the method Insert is missing public Insert(itemtype item, int index); //verifies index & inserts item at position index in list //valid abstract method public int Search (itemtype item); //searches list & returns position of item. Returns -1 if not found //valid abstract method public int CountItem ( itemtype Item); //invalid abstract method   ,methods should be public since //the methods need to implemented in the class //validates that index is position within list private boolean VerifyIndex (int index); } --------------------------------------------------------------------- Correct interface declaration public interface ArrayList { public void Insert(itemtype item, int index); public int Search (itemtype item); public int CountItem ( itemtype Item); public boolean VerifyIndex (int index); } .

1. Given the following interface for a list, comment on it from the perspective of an ADT. Consider
what is in there and what is missing, what is right and what is wrong.
Solution
Note Points of Interface:
Interface provides the declaration of abstract methods that needs to be implemented in the class
by which the interface is implementing.
Interface does not have a construcor.It contains the abstract method declaration and static
constants.
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//Comments are provide which is valid and invalid methods
public interface ArrayList
{
//It is not valid since the class implementing the interface will have to implement only methods
//not class constructor
//Invalid declaration
// public ArrayList(void) { List = 0 };
//constructor - initializes list to be empty
//Invalid abstract method since the return type of the method Insert is missing
public Insert(itemtype item, int index);
//verifies index & inserts item at position index in list
//valid abstract method
public int Search (itemtype item);
//searches list & returns position of item. Returns -1 if not found
//valid abstract method
public int CountItem ( itemtype Item);
//invalid abstract method  ,methods should be public since
//the methods need to implemented in the class

2. //validates that index is position within list
private boolean VerifyIndex (int index);
}
---------------------------------------------------------------------
Correct interface declaration
public interface ArrayList
{
public void Insert(itemtype item, int index);
public int Search (itemtype item);
public int CountItem ( itemtype Item);
public boolean VerifyIndex (int index);
}