1Arrays11/14/20072Opening Discussion■Let's look at solutions to the interclass problem.■Sitting and listening vs. following along.3Collections of Objects■We saw in Alice how there are situations where we needed to have collection of different things.■This is a general need in programming. We need to have some simple way of dealing with multiple objects.■Java actually provides many ways for dealing with these collections of objects.■Today we begin with the one type of collection actually built into the language instead of the libraries: arrays.4Arrays■Just like in Alice, an array in Java is a fixed length collection of things. Unlike Alice, arrays work well in Java.■We can make an array type by placing square brackets after any type in Java.int[] a;String[] strs;■Arrays are reference types so we need to instantiate them. During instantiation we tell Java how large the array is.a=new int[10];strs=new String[6];5Using Arrays■We get the elements out of an array by placing an integer expression in the square brackets after a variable name.a[7]=5;■The indexes go from zero to the length minus one.■Arrays know their length and you can get it with the length property.■It is common to have loops that run through the contents of arrays.for(int i=0; i<a.length; i++) { ... }6Multidimensional Arrays■You can make arrays of arrays (or arrays of those). The syntax is just a logical extension of the 1-D arrays.int[][] a2;String[][] strs2;■We can allocate rectangular 2-D arrays with a simple syntax as well.a2=new int[10][20];strs2=new String[5][4];7Code■Let's use an array inside of our payroll application.8Minute Essay■Write a method that takes an array of ints and returns the sum of all the elements in the array.■Interclass Problem – Do problem 12.2. You can put a number at the top of the file so that it is easy to store all the friends in an
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