Java Data Structure - Arrays.

Arrays

• Array is aggregate data types that contains elements of the items in an array.
• Built-in in Java for primitives or references.
• Jagged array vs Retangular array
• Enhanced for loop
• Array Class: java.util.Arrays
• fill (arrayName, value) // Fill out all elements to "value"
• fill (arrayName, fromIndex, toIndes_plus_1, value)
• equals (array1, array2)
• copyOf (arrayFrom,  length) // JDK 1.6+ shallow copy for ref type
• copyOfRange (arrayFrom,  fromIndes, toIndex_plus_one) // JDK 1.6+
• sort (arrayName) // MUST implememts Comparable Interface
• sort (arrayName, fromIndex, toIndex)
• binarySearch (arrayName, value) // Must have compareTo, sort or binarySearch method defined and must do Arrays.sort first for binarySearch

Example

String [] sArray;
String sArray[];
sArray = new String[];
sArray = new String[10];
sArray = new String[10][];

String [] SArray = new String[];
String sArray [] = {"Mary", "Susan", "Raymond"};
double [] dArray = new double[10];
double [] prices = {12.95, 11.95, 10.95};

final int TOTAL_STUDENTS = 50;
Scanner sc = new Scanner(System.in);
int totalStudents = sc.nextInt();
String [] StudentsA = new String[TOTAL_STUDENTS];
String [] StudentsB = new String[totalStudents];

StudentsA[0] = "Mary";

String[] name1 = {"Forrest Gump", "A Beautiful Mind"};
String[] name2 = {"Forrest Gump", "A Beautiful Mind"};
// if (name1 == name2) ==> gives "false"
// if (Arrays.equals(name1, name2) ==> gives "true"

Public interface Comparable {
    int compareTo (Object obj);
}

class Item implements Comparable {
    private int number;
    private String name;
    public Item (int n, String s) {
        this.number = n;
        this.name = s;
    }

    public int getNumber () {
        return number;
    }

    // This overriding compareTo compares the first field
    //     which is the item.number in this case
    //     can be altered by supplementing with another
    //     class implementing "Comparator" interface
    //     to compare by name
    //
    @Ovrride
    public int compareTo(Object o) {
        if (o instanceof Item) {
            Item i = (Item) o;
            if (this.getNumber() < i.getNumber()) {
                return -1;
            } else if (this.getNumber() > i.getNumber()) {
                return 1;
            }
            return 0; 
        }
    }
}

public class ItemOtherCompare implements Comparator {
    public int compare (Object o1, Objece o2) {
        int i1 = ((Item) o1).getOtherField();
        int i2 = ((Item) o2).getOtherField();
        if (i1 > i2) return 1;
        if (i2 > i2) return -1;
        return 0;
    }

    public boolean equals (Object o1, Object o2) {
        int i1 = ((Item) o1).getOtherField();
        int i2 = ((Item) o2).getOtherField();
        return (i1 == i2);
        return false;
    }
}

// Arrays.sort(items); // this will sort by first field data
// Arrays.sort(items, new ItemOtherCompare()); // this will sort by other field