JAC444: Intro to Java Arrays and Vectors

1. JAC444: Intro to Java Arrays and Vectors Tim McKenna Seneca@York

2. Arrays in Java • arrays are objects • declare an array object reference • int[] iAr; String[] strAr; // i.e. type[] • new creates an array object • specify the number of elements • iAr = new int[3]; strAr = new String[5]; • auto initialization of array elements • primitive types: zero value • reference type: null

3. Arrays in Java • length: public final instance variableiAr.length == 3; strAr.length == 5; • compile-time or runtime assignment of array element values • java.util.Arrays – utility methods to • copy, search, sort, fill, convert toString • ArrayIndexOutBoundException • Example: ArrayDemo.java, ArrayDemoStrings, ArrayDemoObjects

4. Two-Dimensional Arrays • an array of arrays (i.e. an array of objects) • an irregular / unbalanced array • Examples: ArrayDemo2.java ArrayDemo3.java

5. VectorClass • Java package: java.util, • part of the Java Collection Framework • vector: like an array that shrinks and grows • vector stores generic object references • ArrayList class is like a Vector but is not synchronized – less overhead for the JVM. • must be synchronized to support Threads

6. Vector Class • useful methods: • isEmpty(), size() • add(), remove(), insertElementAt() • get(), set() • methods using the object's equals() method: contains(), indexOf(), lastIndexOf(), remove() • Examples: VectorDemoObjects.java, VectorDemoCars.java, ParkingLot.java, ParkingLotCars.java

7. Collections passing • do not give out references to your collection – preserve encapsulation • java.util.Collections.unmodifiableXXX • allows modules to provide users with "read-only" access to internal collections.