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Arrays

Arrays. What is an array?. An array is a group of items all of the same type which are accessed through a single identifier. int[] nums = new int[ 10 ];. 0 1 2 3 4 5 6 7 8 9. nums. Array References. int[] nums;. nums. null. null. nothing.

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Arrays

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  1. Arrays

  2. What is an array? An array is a group of items all of the same type which are accessed through a single identifier. int[] nums = new int[10]; 0 1 2 3 4 5 6 7 8 9 nums

  3. Array References int[] nums; nums null null nothing nums is a reference to an integer array.

  4. Array Instantiation new int[3]; 0x213 arrays are Objects.

  5. Arrays int[] nums = new int[3]; nums 0x213 0x213 nums is a reference to an integer array.

  6. Strings are arrays String s = "compsci"; //Strings are arrays 0 1 2 3 4 5 6 s The first index position in a String is 0. A String is an array of characters.

  7. Arrays int[] nums = new int[10]; //Java int array 0 1 2 3 4 5 6 7 8 9 nums Arrays are filled with 0 values when instantiated. The exact value of each spot in the array depends on the specified type for the array.

  8. Arrays int[] nums = new int[10]; //Java int array 0 1 2 3 4 5 6 7 8 9 nums The size must always be an int.

  9. Arrays int[] nums = {2,7,8,234,745,1245}; 0 1 2 3 4 5 nums An array can be initialized with values.

  10. Indexes 0 1 2 3 4 5 6 7 8 9 nums The [spot/index] indicates which value in the array is being manipulated. nums[0] = 9; The 0 spot is being set to 9.

  11. Indexes Java indexes must always be integers and the first index will always be 0. 0 1 2 3 4 5 6 7 8 9 nums

  12. Array Constant Length • Unlike String who uses a method to return the length of the string… String name = “Furman”; int len = name.length(); //len is 6 • Arrays use a length constant. The length of an array can not change once it is created. int[] nums = { 1, 2, 3}; int numsLen = nums.length; // len = 3 • Notice that the method length() is followed by parenthesis, while the constant length is not!!

  13. Printing Arrays

  14. Printing arrays int[] nums = {1,2,3,4,5,6,7}; System.out.println(nums[0]); System.out.println(nums[1]); System.out.println(nums[2]); System.out.println(nums[5]); OUTPUT1236 0 1 2 3 4 5 6 nums

  15. Printing arrays int[] nums = {1,2,3,4,5,6,7}; for(int spot=0; spot<nums.length; spot++) { System.out.println(nums[spot]); } OUTPUT1234567 length returns the # of elements/items/spots in the array!!!

  16. Printing arrays int[] nums = {1,2,3,4,5,6,7}; for(int item : nums) { System.out.println(item); } OUTPUT1234567 0 1 2 3 4 5 6 nums

  17. //array output example 1 import static java.lang.System.*; public class ArrayOutOne { public static void main(String args[]) { int[] nums = {1,2,3,4,5,6,7}; System.out.println(nums[0]); System.out.println(nums[1]); System.out.println(nums[2]); System.out.println(nums[5]); } }

  18. //array output example 2 import static java.lang.System.*; public class ArrayOutTwo { public static void main(String args[]) { int[] nums = {1,2,3,4,5,6,7}; //add in a for loop to print out nums System.out.println("\n\n"); //another bug to fix - what is the problem? int[] intList = null; //add in a for loop print out intList } }

  19. Setting Array Spots

  20. Setting array spots int[] nums = new int[10]; nums[0] = 231; nums[4] = 756; nums[2] = 123; System.out.println(nums[0]); System.out.println(nums[1]); System.out.println(nums[4]); System.out.println(nums[4/2]); OUTPUT 2310756123

  21. Setting array spots double[] nums = new double[10]; nums[0] = 10.5; nums[3] = 98.6; nums[2] = 77.5; System.out.println(nums[0]); System.out.println(nums[3]); System.out.println(nums[7]); OUTPUT 10.598.60.0

  22. Setting array spots int[] nums = new int[6]; for(int spot=0; spot<nums.length; spot++) { nums[spot] = spot*4; } 0 1 2 3 4 5 nums

  23. //array set example 1 import static java.lang.System.*; public class ArraySetOne { public static void main(String[] args) { int[] nums = new int[10]; //all spots set to zero to start nums[0] = 231; nums[4] = 756; nums[2] = 123; System.out.println(nums[0]); System.out.println(nums[1]); System.out.println(nums[4]); System.out.println(nums[4/2]); } }

  24. //array set example 2 import static java.lang.System.*; public class ArraySetTwo { public static void main(String[] args) { int[] nums = new int[6]; for(int spot=0; spot<nums.length; spot++) { nums[spot] = spot*4; } for(int spot=0; spot<nums.length; spot++) { System.out.println(nums[spot]); } } }

  25. Arrays as Instance Variables

  26. Instance Variables public class Array { private int[] nums; //has the value null public Array(){ nums = new int[10]; //sizes the array } //other methods not shown }

  27. toString() public class Array { //instance vars and other methods not shown public String toString() { String output= ""; for(int spot=0; spot<nums.length; spot++) { output=output+nums[spot]+" "; } return output; } }

  28. toString() public class Array { //instance vars and other methods not shown public String toString() { String output= ""; for( int val : nums ) { output = output + nums + " "; } return output; } }

  29. InstanceVarsTwo String list = "7 6 3 4 9 1 3 5"; int[] nums = new int[8]; Scanner chopper = new Scanner(list); int spot=0; while(chopper.hasNextInt()) { nums[spot++]=chopper.nextInt();}

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