Java Array CheatBook for Programming Questions.
Just like in any other programming language, an Array in Java is a collection of similar types of elements with contiguous memory allocation.
The array type directly extends Object class. Every array type implements the interfaces Cloneable and java.io.Serializable.
An array can store a fixed set of elements. In Java, Arrays are index-based, more particularly 0-indexed. This means the indexing in arrays begins from 0. One important difference to begin off the comparison to C/C++ arrays is the ‘length’ attribute. In size the size of the array i.e. the number of elements present in the array can be found using arrayName.length attribute.
Types of Arrays In Java: Single Dimensional and MultiDimensional
Syntax to Declare:
dataType[] arrayName;
or
dataType arrayName[];
Syntax To Instantiate:
dataType arrayRefVariable = new dataType[size];
For-Each Loop for Java Array:
for( dataType variable: array) {
//Code Here
}
Passing and Returning Array to a Method in Java:
class TestArray{
public static void Fun(int arr[]){
int low=arr[0];
int high=arr[arr.length-1];
}
public int[] returnArray(int arr[]){
for(int i=0;i<arr.length;++i){
arr[i]+=10;
}
return arr;
}}
Anonymous Array in Java
public class TestAnonymousArray{
public static void Fun(int arr[]){
for(int i=0;i<arr.length;++i){
System.out.println(arr[i]);
}
public static void main(String[] args){
Fun(new int[]{1,2,3,4,5,6});
}
}
Jagged Array
Jagged Array is an Array with unequal number of columns. Jagged Array’s concept implies over multidimensional arrays. A multidimensional array in general words can be thought of an array with another array in every index position.
Copying A Java Array:
System class in java offers an arrayCopy(Object src, int srcPos, Object dest, int destPos, int length) method to copy one array to another.
Syntax:
arraycopy(Object src, int srcPos,Object dest, int destPos, int length)
Example:
class TestCopyArray{
public static void main(String[] args){
char arr[]={‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’};
char arr2[] = new char[5];
System.arraycopy(arr,0,arr2,0,5);
}
}
Cloning an Array:
int arrOriginal={1,2,3,4,5,6,7,8,9};
int arrCloned[]=arr.clone();
for(i:arrCloned){
print(i);
}
Arrays Class in Java:
Package: java.util
Arrays is a part of Java Collections Framework. It give methods for dynamic creation of arrays and accessing arrays.
Syntax to Use:
Arrays.<FunctionToBeUsed>
BinarySearch in Array
static int binarySearch(elementToBeSearched)
int arr={10,20,30,40,50,60};
Arrays.sort(arr);
int key=30;
int index=Arrays.binarySearch(arr,key);
Binary Search in Range:
int arr={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19};
Arrays.sort(arr);
int index=Arrays.binarySearch(arr,0,9,19);
//0: index to start, 9: index to search till, 19: key
Arrays.compare:
int a={1,2,3,4,5,6,7,8,9};
int b={1,6,9}
System.out.println(Arrays.compare(a,b));// Prints 1
