String[] names = new String[16]; arr.length; list.size(); str.length();

Week 3: Objects, files and exceptions/9a. Data structure - ARRAY

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+Arrays are static data structures: their SIZE is defined AT INITIALISATION and cannot be changed afterwards. 
+It is therefore not possible to add or remove primitives from an array. 
+In general, a list is a more useful structure, but some Java methods return an array- so it's a good idea to know how to use them.
+
+
+
+// datatype of elements
+// empty square brackets []
+// variable name
+// 'new' operator - define the array object
+// datatype of elements
+// num_elements
+
+public class Example {
+    public static void main(String[] args){
+        // Array in which 10 integers
+        // can be saved
+        int[] numarray = new int[10];
+
+        // Array for strings
+        String[] names = new String[20];
+
+        // Array for floating-point numbers
+        double[] results = new double[5];
+    }
+}
+
+
+At initialisation, fill array with default values
+- integer 0
+- boolean false
+- null
+
+
+
+VS
+
+
+// initialise Array with values
+// Array with five integers
+int[] numarray = {1, 3, 2, 5, -1};
+
+// Array with strings
+String[] names = {"Jack", "Pete", "Jane", "Lisa"};
+
+// Array with floating-point numbers
+double[] results = {1.0, 2.5, 0.75};
+
+
+
+
+
+======================================================
+
+
+
+
+
+import java.util.Arrays;
+
+public class Example {
+    public static void main(String[] args){
+        int[] numbers = new int[5];
+        numbers[0] = 10;             // variableName[idx]
+        numbers[1] = 40;
+        numbers[4] = -155;
+
+        // When printing an array the method 
+        // Arrays.toString is useful.
+        System.out.println(Arrays.toString(numbers)); // [10, 40, 0, 0, -155]
+
+
+        double[] heights = {175.5, 150.75, 201.05};
+        System.out.println(heights[0]);
+        
+        heights[1] = heights[1] + 10;    // variableName[idx]
+        System.out.println(heights[1]);  // variableName[idx]
+    }
+}
+
+
+Program outputs:
+[10, 40, 0, 0, -155]
+175.5
+160.75
+
+
+
+
+
+
+
+
+======================================================
+
+
+length
+
+
+
+
+
+The length of the array (i.e. the number of sub-arrays) is determined by the length attribute. 
+The extended for clause can also be used to iterate through an array in the same way as iterating through a list.
+
+import java.util.Arrays;
+
+public class Example {
+    public static void main(String[] args){
+        int[] numbers = {1,2,3,4,5,6,7};
+        System.out.println("Array length: " + numbers.length);
+
+        for (int element : numbers) {
+            System.out.println(element);
+        }
+
+        for (int i=0; i<numbers.length; i++) {
+            numbers[i]++;
+        }
+
+        System.out.println(Arrays.toString(numbers));
+    }
+}
+
+Program outputs:
+Array length: 7
+1
+2
+3
+4
+5
+6
+7
+[2, 3, 4, 5, 6, 7, 8]
+
+
+
+
+
+
+
+
+======================================================
+
+
+
+
+
+
+Note that unlike a string, ARRAY LENGTH is an attribute
+ARRAY length is not a method - it is not followed by parentheses. 
+
+
+
+The example below further illustrates the differences between length detection for a string, an array and a "list":
+
+int[] array = {1,2,3,4,5,6,7};
+
+ArrayList<Integer> list = new ArrayList<>();
+list.add(1);
+list.add(2);
+
+String str = "Hey";
+
+System.out.println("Array length: " + array.length);
+System.out.println("List length: " + list.size());
+System.out.println("String length: " + str.length());
+ 
+
+Program outputs:
+Array length: 7
+List length: 2
+String length: 3
+
+
+
+
+
+
+
+