Lecture 22

Generic Methods

• method with a type parameter
• independent of a generic class
• can be used in a non-generic class
• can be used in a generic class with a different type parameter

public class myClass
{
public void myMethod(T x)
{
System.out.println(x);
}
}

• syntax for calling the method

myClass m = new myClass();
m.myMethod("Hello");
m.myMethod(6);


Inheritance

• inheritance is allowed with generics

public class Parent
{
}


public class Child extends Parent
{
public class A {...}
public class myGeneric{...}
myGeneric//these two have
myGeneric//No Relationship

ArrayList

• ArrayList is a generic class that handles arrays of arbitrary and changeable size
• must be imported
• import java.util.ArrayList;

Example

Create an array of 5 Strings using ArrayList


ArrayList myList = new ArrayList(5);
// = generic type parameter

• Array
• String[] A = new String[s];
• a[3] = "Hello"
• String b = a[z]
• int len = a.length
• ArrayList
• ArrayList myList = new ArrayList(5)
• myList.set(3,"hello")
• String b = myList.get(2);
• int len = myList.size()
• 
  
• Both Indexes start at zero

• unlike an array you can add elements to an ArrayList

ArrayList myList = new ArrayList(0);//size is 0
myList.add("x"); // size is now 1
myList.add("y"); // puts y at index 1, size is now 2

• Can add to the beginning as a middle of the ArrayList
• myList.add(0, "w")
• "w" = 0, "x" = 1, "y" = 2
• myList.add(1,"q")
• "w"=0, "q" = 1, "x "= 2, "y"= 3