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JAC444: Intro to Java Arrays and Vectors Tim McKenna Seneca@York 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 Arrays in Java length: public final instance variable iAr.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 Two-Dimensional Arrays an array of arrays (i.e. an array of objects) an irregular / unbalanced array Examples: ArrayDemo2.java ArrayDemo3.java Vector Class 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 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 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.