ArrayList

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ArrayList
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java.util.ArrayList

• Everything stored must be an Object
• Objects can be different types
• Size is dynamic, rather than fixed.
• Provides methods for adding and removing

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Methods in ArrayList class
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ArrayList

• Stored elements may be of different types
• Example Objects of type Animal, Vegetable, and
  Mineral could all be stored in ArrayList. (Object
  is a superclass of Animal, Vegetable and Mineral.
  All are of type Object)

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ArrayList

• Need to be concerned about type returned by
  ArrayList method.
• Notice Return type for get, set and remove are
  of type Object. If the returned object is to be
  used with a particular class, it needs to be cast
  to that class type.

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ArrayList

• Primitives cannot be stored in an ArrayList.
• Use the wrapper classes Integer and Double
• public static ArrayList setScores(int numTests)
• ArrayList scores new ArrayList()
• for (int k 0 k lt numTests k)
• int aScore readInt()
• scores.add(new Integer(aScore)

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Print the scores

• public static void printScores(ArrayList scores)
• for (int k 0 k lt scores.size() k)
• System.out.println(scores.get(k)

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Print the highest score

• public static Integer getMaxScore(ArrayList
  scores)
• //assume first element is max score
• Integer max (Integer)scores.get(0)
• for(k 1 k lt scores.size() k)
• Integer temp (Integer)scores.get(k)
• if(temp.compareTo(max) gt 0)
• max temp
• return max

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Understand?

• ArrayList names new ArrayList()
• names.add(Alex)
• names.add(Sam)
• names.add(0, Tasha)
• names.add(2, Randy)
• names.add(2, Sandy)
• names.add(2, Mandy)
• names.remove(0)
• names.remove(2)

• Tasha, Alex, Mandy
• Sam, Mandy, Randy
• Mandy, Sandy, Randy, Sam
• Alex, Mandy, Randy, Sam
• NoSuchElement Exception

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Wrapper classes

• Primitive data types cannot be stored in an
  ArrayList - elements must be Objects
• Use Integer and Double used to wrap primitive
  values in an object.
• Method
• compareTo(Integer intObject)
• intValue()