Arrays

Question 1

Declare an array

Answer 1

• String[] aArray = new String[5];
• String[] bArray = {“a”,”b”,”c”, “d”, “e”};
• String[] cArray = new String[]{“a”,”b”,”c”,”d”,”e”};

Question 2

ArrayList from an Array

Answer 2

• String[] stringArray = { “a”, “b”, “c”, “d”, “e” };
• ArrayList<string> arrayList = </string>

new ArrayList<string>(Arrays.asList(stringArray));</string>

Question 3

Check if an Array contains a value

Answer 3

• String[] stringArray = { “a”, “b”, “c”, “d”, “e” };
• boolean b = Arrays.asList(stringArray).contains(“a”);

Question 4

Array from ArrayList

Answer 4

• String[] stringArray = { “a”, “b”, “c”, “d”, “e” };
• ArrayList<string> arrayList = </string>

new ArrayList<string>(Arrays.asList(stringArray)); </string>

• String[] stringArr = new String[arrayList.size()];
• arrayList.toArray(stringArr);

Question 5

List from an Array

Answer 5

• List<string> stooges = Arrays.asList("Larry", "Moe", "Curly");</string>

Question 6

fill(int[] a, int val)

Answer 6

• Assigns the specified int value to each element of the specified array of ints.
• fill(int[] a, int fromIndex, int toIndex, int val)
• Assigns the specified int value to each element of the specified range of the specified array of ints. The range to be filled extends from index fromIndex, inclusive, to index toIndex, exclusive. (If fromIndex==toIndex, the range to be filled is empty.)
• Applies to long, short, char, byte, boolean, double, float and object arrays

Question 7

binarySearch(int[] a, int key)

Answer 7

• Searches the specified array of ints for the specified value using the binary search algorithm. The array must be sorted (as by the sort(int[]) method) prior to making this call.
• Applies to long, short, char, byte, boolean, double, float and object arrays

Question 8

copyOfRange(int[] original, int from, int to)

Answer 8

• Copies the specified range of the specified array into a new array and returns it.
• Applies to long, short, char, byte, boolean, double, float and object arrays

Question 9

copyOf(int[] original, int newLength)

Answer 9

• Copies the specified array, truncating or padding with zeros (if necessary) so the copy has the specified length
• Returns: a copy of the original array, truncated or padded with zeros to obtain the specified length
• Applies to long, short, char, byte, boolean, double, float and object arrays

Question 10

Arrays.sort() with comparator

Answer 10

1. Arrays.sort(words, (a, b)->a.length() - b.length()); // words is string array
2. This way we can even sort string arrays.

Question 11

sort(int[] a)

Answer 11

• Sorts the specified array into ascending numerical order.
• Applies to long, short, char, byte, boolean, double, float and object arrays

Question 12

sort(int[] a, int fromIndex, int toIndex)

Answer 12

• Sorts the specified range of the array into ascending order.
• Applies to long, short, char, byte, boolean, double, float and object arrays

Question 13

deepEquals(Object[] a1, Object[] a2)

Answer 13

• Returns true if the two specified arrays are deeply equal to one another. Unlike the equals(Object[],Object[]) method, this method is appropriate for use with nested arrays of arbitrary depth.
• Two array references are considered deeply equal if both are null, or if they refer to arrays that contain the same number of elements and all corresponding pairs of elements in the two arrays are deeply equal.
• Two possibly null elements e1 and e2 are deeply equal if any of the following conditions hold:

e1 and e2 are both arrays of object reference types, and Arrays.deepEquals(e1, e2) would return true

e1 and e2 are arrays of the same primitive type, and the appropriate overloading of Arrays.equals(e1, e2) would return true.

e1 == e2

e1.equals(e2) would return true.

• Note that this definition permits null elements at any depth.

Question 14

Print an array

Answer 14

• Array.toString(array);