Section 5.5. Arrays

5.5. Arrays

The java.lang.System class defines an arraycopy( ) method that is useful for copying specified elements in one array to a specified position in a second array. The second array must be the same type as the first, and it can even be the same array:

 char[] text = "Now is the time".toCharArray(); char[] copy = new char[100]; // Copy 10 characters from element 4 of text into copy, starting at copy[0] System.arraycopy(text, 4, copy, 0, 10); // Move some of the text to later elements, making room for insertions System.arraycopy(copy, 3, copy, 6, 7); 

In Java 1.2 and later, the java.util.Arrays class defines useful array-manipulation methods, including methods for sorting and searching arrays:

 import java.util.Arrays; int[] intarray = new int[] { 10, 5, 7, -3 }; // An array of integers Arrays.sort(intarray);                       // Sort it in place int pos = Arrays.binarySearch(intarray, 7);  // Value 7 is found at index 2 pos = Arrays.binarySearch(intarray, 12);     // Not found: negative return value // Arrays of objects can be sorted and searched too String[] strarray = new String[] { "now", "is", "the", "time" }; Arrays.sort(strarray);   // sorted to: { "is", "now", "the", "time" } // Arrays.equals() compares all elements of two arrays String[] clone = (String[]) strarray.clone(); boolean b1 = Arrays.equals(strarray, clone);  // Yes, they're equal // Arrays.fill() initializes array elements byte[] data = new byte[100];          // An empty array; elements set to 0 Arrays.fill(data, (byte) -1);         // Set them all to -1 Arrays.fill(data, 5, 10, (byte) -2);  // Set elements 5, 6, 7, 8, 9 to -2 

Arrays can be treated and manipulated as objects in Java. Given an arbitrary object o , you can use code such as the following to find out if the object is an array and, if so, what type of array it is:

 Class type = o.getClass(); if (type.isArray()) {   Class elementType = type.getComponentType(); }