Java SE: Programming Complete - 8

https://learn.oracle.com/ols/course/java-se-programming-complete/82508/85200

Arrays and Loops

Arrays

• An array is a fixed-length collection of elements of the same type indexed by int
• Declare array: int[] primes; or int primes[]
• Create array: primes = new int[4]
  • Once an array is created, its length can’t be changed.
  • An array of object reference is filled with null values
  • An array of primitive values is filled with 0 values (or false for boolean)
• Combined Declaration and Creation int[] primes = new int[3]
• Combined create of the array object and initialization of the array content:

int[] primes;
primes = new int[]{1, 2, 3};

• Combined declaration and creation of the array object as well as the initialization fo the array content: Product[] products = {new Product("Cake"), new Product("Tea"), new Product("Beer")};

Multidimensional Arrays

• Can be of non-square shapes int[][] matrix = { {4, 1}, {2, 0, 5} };
• Can have more than two dimensions

Copying Array Content

• Java arrays are of fixed length (can’t be resized)
• However, resize can be emulated by creating a new array with a different size and copying all or partial content from the original array to the new array object, using System.arrayCopy(<source array>, <source position>, <dest array>, <dest position>, <length>) or <new array> = Arrays.copyOf(<source array>, <new array length>) or <new array> = Arrays.copyOfRange(<source array>, <start position>, <end position>)

Arrays Class

• The java.util.Arrays class provides convenience methods for handling arrays, such as:
  • Filling array with values Arrays.fill
  • Searching through the array Arrays.binarySearch
  • Comparing content Arrays.equals
  • Sorting array content using Comparable or Comparator

Break and Continue

• You can give a loop with a label.
• break terminates the current loop.
• break <label> terminates the labeled loop.
• continue operator skips the current loop cycle.
• continue <label> skips the labeled loop cycle.

char[][] matrix = { {'A', 'B', 'C', 'D', 'E'},
                    {'F', 'G', 'H', 'I', 'K'},
                    {'L', 'M', 'N', 'O', 'P'},
                    {'Q', 'R', 'S', 'T', 'U'},
                    {'V', 'W', 'X', 'Y', 'Z'} };
StringBuilder txt = new StringBuilder();
outerLoopLabel:
for (char[] row : matrix) {
  for (char value: row) {
    if (value == 'C') { continue; }
    if (value == 'H') { continue outerLoopLabel; }
    if (value == 'N') { break; }
    if (value == 'S') { break outerLoopLabel; }
    txt.append(value);
  }
  txt.append('\n');
}

The output of this code is ABDE\nFGLM\nQR;