Example Arrays Write a program to keep track of all students 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 the same type Size is determined at time of declaration Example scores 90 5 73 87 double scores new double 14 Example scores declare the array double scores new double 3 put 90 5 in the first box Example scores 90 5 declare the array double scores new double 3 put 90 5 in the first box scores 0 90 5 1 Example Alternative double scores 90 5 73 87 scores 90 5 73 87 declare the array double scores new double 3 put 90 5 in the first box scores 0 90 5 scores 1 73 scores 3 87 Initializes elements of the array to values given when array is created Subscripts Subscript describes which box of the array you are dealing 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 which produces an integer Example scores 90 5 73 87 assume i 2 sum scores 1 scores 2 sum scores 1 scores i 8 scores 2 scores 1 6 scores i scores i 5 If subscript specified does not exist runtime error ArrayIndexOutOfBoundsException Accessing Array Elements Print all elements of the array scores Accessing Array Elements Print all elements of the array scores Use only one System out println statement Use only one System out println statement double scores 90 5 73 82 for int i 0 i 3 i System out println Score i 1 scores i 2 foreach double 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 an array Passing Array Elements Passing Array Elements Write a method to add two elements of an array Write a method to add two elements of an array How is the method called double add double num1 double num2 return num1 num2 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 a method Example sum scores Sum all elements prompt user for values static double sum double scores double sum 0 for double d scores sum d return sum 3 Arrays of objects Flight flights new Flight 10 Multidimensional Arrays double warmups new double 14 30 Declares a multidimensional array with 14 rows and 30 columns 0 1 2 29 0 1 13 Example 0 1 2 Example 29 0 0 1 1 2 13 29 0 1 13 Set first warmup score for first student to 3 Example 0 1 2 Set first warmup score for first student to 3 warmups 0 0 3 Example 29 Print all scores for all students 0 1 13 Print all scores for all students static 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 4 ArrayList Like an array but it can dynamically change size Stores object references cannot store primitive types without a wrapper By default not declared to store a particular type ArrayList al new ArrayList Because it is a generic type we can explicitly specify the type ArrayList String stringal new ArrayList String 5
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