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6 Get to know the Java API.md

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6 Get to know the Java API
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2017-10-30

ArrayList

ArrayList is a class in the core Java library (the API).

  • :::Java boolean add(Object elem): Adds the objects parameter to the list(return true).
  • :::Java boolean remove(int index): Removes the object at the index parameter. Returns true if the element was in the list.
  • :::Java boolean remove(Object elem): Removes this object(if it's in the ArrayList).
  • :::Java boolean contains(Object elem): Returns true if there's a match for the object parameter.
  • :::Java boolean isEmpty(): Returns true if the list has no elements
  • :::Java int indexOf(Object elem): Returns either the index of the object parameter, or -1
  • :::Java size(): Return the number of elements currently in the list.
  • :::Java Object get(int index): Return the object currently at the index parameter.

You have to know the full name of the class you want to use in your code. You have two options:

  • Import: put an import statement at the top of your source code file:
    • :::Java import java.util.ArrayList
  • Type: type the full name everywhere in your code. Each time you use it.
    • :::Java java.util.ArrayList<Dog> list = new java.util.ArrayList<Dog>();

Import

An import is not the same as include in C. So the import doesn't make a class bigger. An import statement saves you from typing. That's really it. It simply give Java the full name of a class.

You must tell Java the full name of every class you use, unless that class is in the java.lang package.