Java arrays!

Java Arrays

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class array {
    public static void main(String[] args) { 

        int i,j,k;
        i = j = k = 0;
        System.out.println("demo hello");
        
        int[] nums = new int[20];
        double[] prices = { 5.5, 3, 4.2 };
        boolean[] ans = { true,false,true };
        char[] vowels = { 'a','e','i','o','u' };
        String[] names = new String[10];

        nums[1] = 1;
        nums[2] = 2;
        printarray (nums);
        ArrayList list = new ArrayList<>();
        Arrays.sort (nums);
        Arrays.sort (nums);
        int[][] rents = {{},{},{}};
        
        // ArrayList can only hold Objects
        // ArrayList is a dynamic array
        List<Integer> myiary = new ArrayList<Integer>();
        myiary.add(2);
    }
 
    public static void printarray (int[] a) {
        int j = 0;
        for (int i : a) {
            System.out.printf("s[%d] = %d, " , j,i);
            j++;
            if (j % 5 == 0) {
                System.out.println();
            }
        }
    }
 
    public static void printarray (String[] a) {
        for (String i : a) {
            System.out.printf("%s\n" , i);
        }
    }
}

Java String and Characters

public static void main(String[] args) throws IOException {
    BufferedReader f = new BufferedReader(new FileReader("beads.in"));
    PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("beads.out")));
    StringTokenizer st = new StringTokenizer(f.readLine());
     
    int n = Integer.parseInt(st.nextToken());
    String s = f.readLine();
    char[] sc = s.toCharArray();
    System.out.println(sc);

    char[] chars = {'t','h','i','s',' ','\u0024'};  // \u0024 is $ sign
    String s = new String(chars);
    System.out.println( s );
}

Insert and copy arrays

    public static void copyArray(int[] array, int index) {
         List<Integer> myiary = new ArrayList<Integer>();
         myiary.add(2);

         int[] tmp = new int[array.length-1];
         System.arraycopy( array, 0, tmp, 0, index);

         Integer[] iarray = new Integer[] { 2,3,4 };
         List<Integer>> iiarray = new ArrayList<Integer>() {{
             add(1);add(2);add(3);
         }};
    
         List<Integer> list = new ArrayList<Integer>(Arrays.asList(iarray));
         List<Integer> iilist = new ArrayList<Integer>(iiarray);

         ArrayList<String> slist = new ArrayList<String>(Arrays.asList(
             new String[] {"One","Two","Three","Four"}));
    }

Modify and merge elements in arrays

    String a[] = { "A", "E", "I" };
    String b[] = { "O", "U" };
    List list = new ArrayList(Arrays.asList(a));
    list.addAll(Arrays.asList(b));
    Object[] c = list.toArray();
    System.out.println(Arrays.toString(c));

    int[] ia = {1,2,3};
    int[] ib = {4,5,6};
    int[] ic = new int[ ia.length + ib.length ];
    // use loop to concatenate ia, ib to ic

Slice the array

    public static void sliceArray() {
        // intializing an array arr1
        byte[] arr1 = new byte[] {5, 62, 15};

        // printing the array arr1
        System.out.println("Printing 1st array:");
        for (int i = 0; i < arr1.length; i++) {
            System.out.println(arr1[i]);  
        }

        // copying array arr1 to arr2 with range from index 1 to 7
        byte[] arr2 = Arrays.copyOfRange(arr1, 1, 7);

        // printing the array arr2
        System.out.println("Printing new array:");
        for (int i = 0; i < arr2.length; i++) {
            System.out.println(arr2[i]);
        }
    }

Remove elements in arrays

    public static void removeElement(Integer[] array, int index) {
        int[] tmp = new int[array.length-1];
        System.arraycopy( array, 0, tmp, 0, index);

        List<Integer> list = new ArrayList<Integer>(Arrays.asList(array));
        list.add(3);
        list.add(4);
        for (int i = 0; i < list.size(); i++) {
            if (list.get(i).equals(index)) {
                list.remove(i);
            }
        }
    }

Looping over the array

    for (<type> i : array_of_type) {
    }
    char[] chars = {'t','h','i','s',' ','\u0024'};
    // char to string
    String s = new String(chars);
    // string to char
    char[] chars2 = s.toCharArray();
    for (char c : chars) { System.out.print(c); }
    System.out.println();

Using Java 8 Stream API

    List<String> nums = Stream.of("ONE", "TWO", "THREE", "FOUR")
        .collect(Collectors.toList());

Using Java 8 Collections API

    List<String> places = Collections.unmodifiableList
        (Arrays.asList("One", "Two", "Three"));

Using Java 9 API

    List<String> sary = List.of("One", "Two", "Three");
    List<Integer> iary = List.of(1,2,3);

Using Class for Arrays

import java.util.*;
import java.util.Arrays;

public class ary
{
    public static void main (String[] args) {
        int iary1[] = { 1,2,3,4 };
        int iary2[] = { 5,6,7,8 };
        int iary3[] = Arrays.copyOf (iary2, 10);
        int iary4[] = Arrays.copyOfRange (iary3, 1, 3);
        int iary5[] = { 6,2,7,0,1,3,4 };

        System.out.println ("arrays:");
        System.out.println ( Arrays.toString(iary1));
        System.out.println ("compare two array:");
        System.out.println ( Arrays.equals(iary1, iary1));
        System.out.println ( Arrays.equals(iary1, iary4));

        System.out.println ("array sort:");
        Arrays.sort(iary5);
        System.out.println ( Arrays.toString(iary5));

        int tary1[][] = { { 9,8,7,6,5,4} };
        int tary2[][] = { { 9,6,4 } };
        System.out.println ( "Arrays comparison" );
        System.out.println ( Arrays.deepEquals (tary1, tary2 ));
        // Arrays.compare (iary1, iary2 );
        // Arrays.compareUnsigned (iary1, iary2 );
        // System.out.println ( Arrays.compare (iary1, iary2 ));

        ArrayList list = new MyArrayList("a", "b", "c");
    }
}

public class MyArrayList<T> extends ArrayList<T> {
    public MyArrayList(T... values) {
        super(Arrays.asList(values));
    }
}