1ArraysExample• Write a program to keep track of allstudents’ scores on exam 1.• Need a list of everyone’s score• Declare 14 double variables?• What about next semester?Arrays• Declare a list of variables – all with thesame type• Size is determined at time of declarationdouble[] scores = new double[14];Example90.573 87scores:Example//declare the arraydouble[] scores = new double[3];//put 90.5 in the first boxscores:Example//declare the arraydouble[] scores = new double[3];//put 90.5 in the first boxscores[0] = 90.5;90.5scores:2Example//declare the arraydouble[] scores = new double[3];//put 90.5 in the first boxscores[0] = 90.5;scores[1] = 73;scores[3] = 87;90.573 87scores:Alternativedouble[] scores = {90.5, 73, 87};• Initializes elements of the array to valuesgiven when array is createdSubscripts• Subscript describes which box of the array you aredealing with• Array of size N has subscripts– 0, 1, 2, … (n-1)– array of size 3 – 0, 1, 2– subscript added to base address of array• Subscript can be a variable or expression whichproduces an integer– scores[i];– scores[i+5];• If subscript specified does not exist – runtime error(ArrayIndexOutOfBoundsException)Example//assume i = -2;sum = scores[1] + scores[2];sum = scores[1] + scores[i*8];scores[2] = scores[1] + 6;90.573 87scores:Accessing Array Elements• Print all elements of the array scores– Use only one System.out.println statementAccessing Array Elements• Print all elements of the array scores– Use only one System.out.println statementdouble[] scores = {90.5, 73, 82};for(int i = 0; i < 3; i++) { System.out.println("Score " + (i+1) + ": " + scores[i]);}3foreachdouble[] scores = {90.5, 73, 82};for(double d : scores) { System.out.println("Score " + d);}Passing Array Elements• Write a method to add two elements of anarrayPassing Array Elements• Write a method to add two elements of anarray– How is the method called?double add(double num1, double num2) {return (num1 + num2);}Passing Array Elements• Write a method to add two elements of anarray– How is the method called?add(scores[0], scores[1]);…double add(double num1, double num2) {return (num1 + num2);}Passing Arrays• Would like to pass an entire array into amethod– Sum all elements, prompt user for valuesExamplesum(scores);static double sum(double[] scores) { double sum = 0; for(double d: scores) { sum+=d; } return sum;}4Arrays of objectsFlight[] flights = new Flight[10];Multidimensional Arrays• double[][] warmups = new double[14][30];• Declares a multidimensional array with 14rows and 30 columns…01130 1 2 29Example• Set first warmup score for first student to3…01130 1 2 29Example• Set first warmup score for first student to3warmups[0][0] = 3;…01130 1 2 29Example• Print all scores for all students…01130 1 2 29Example• Print all scores for all studentsstatic void printscores(double[][] scores) { for(int row = 0; row < scores.length; row++) { for(int col = 0; col < scores[row].length; col++) { System.out.println("Item " + scores[row][col]); } }}5ArrayList• Like an array, but it can dynamicallychange size• Stores object references– cannot store primitive types without a wrapper• By default, not declared to store aparticular type– ArrayList al = new ArrayList();• Because it is a generic type, we canexplicitly specify the type– ArrayList<String> stringal = new
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