Array Yoshi

Definition An array is a container object that holds a fixed number of values of a single type. The length of an array is established when the array is created. After creation, its length is fixed.

Note int[] anArray;  declares an array of integers  An array's type is written as type[]  [ ] are special symbols indicating that this variable holds an array.

Examples The following are correct  double[] anArrayOfDoubles;  boolean[] anArrayOfBooleans;  char[] anArrayOfChars;  String[] anArrayOfStrings; In fact, the following can also correct  Double anArrayOfDoubles[];  But it is discouraged!!

Also objects int[] anArray = new int[10];  Note that it uses the keyword new  anArray is a reference type variable to point to an array object  Try it System.out.println( anArray.getClass() ); System.out.println( anArray.length );

Initialization int[] anArray = new int[10];  The content of an array will be initialized to the default values automatically int[] anArray = {100, 200, 300, 400, 500, 600, 700, 800, 900, 1000}; String[][] names = { {"Mr. ", "Mrs. ", "Ms. "}, {"Smith", "Jones"} };  Note that names is a irregular array (not block style)

Irregular Array public class ArrayDemo { public static void main(String[] args) { int[][] array = new int[3][]; array[0] = new int[8]; array[1] = new int[5]; array[2] = new int[10]; System.out.println(array.length); //3 System.out.println(array[0].length); //8 System.out.println(array[1].length); //5 System.out.println(array[2].length); //10 }

Copying Arrays The System class has an arraycopy method that you can use to efficiently copy data from one array into another  public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length) Of course, we can write a loop to do it by ourself

Example class ArrayCopyDemo { public static void main(String[] args) { char[] copyFrom = { 'd', 'e', 'c', 'a', 'f', 'f', 'e', 'i', 'n', 'a', 't', 'e', 'd' }; char[] copyTo = new char[7]; System.arraycopy(copyFrom, 2, copyTo, 0, 7); System.out.println(new String(copyTo)); }

For more array operations java.util.Arrays  Arrays.html Arrays.html  Such as sorting, binary search, etc

Pitfall Student[] students = new Student[10]; System.out.println(students[0]);  What’s the output?