Array is a container which can hold a fix number of items and these items should be of the same type. Most of the data structures make use of arrays to implement their algorithms. Following are the important terms to understand the concept of Array.
- Element: Each item stored in an array is called an element.
- Index: Each location of an element in an array has a numerical index, which is used to identify the element.
Creating object arrays
Yes, since objects are also considered as datatypes (reference) in Java, you can create an array of the type of a particular class and, populate it with instances of that class.
Example
Following Java example have a class named Std and later in the program we are creating an array of type Std, populating it, and invoking a method on all the elements of the array.
class Std {
private static int year = 2018;
private String name;
private int age;
public Std(String name, int age){
this.name = name;
this.age = age;
}
public void setName(String name) {
this.name = name;
}
public void setAge(int age) {
this.age = age;
}
public void display(){
System.out.println("Name: "+this.name);
System.out.println("Age: "+this.age);
System.out.println("Year: "+Std.year);
}
}
public class Sample {
public static void main(String args[]) throws Exception {
//Creating an array to store objects of type Std
Std st[] = new Std[4];
//Populating the array
st[0] = new Std("Bala", 18);
st[1] = new Std("Rama", 17);
st[2] = new Std("Raju", 15);
st[3] = new Std("Raghav", 20);
//Invoking display method on each object in the array
for(int i = 0; i<st.length; i++) {
st[i].display();
System.out.println(" ");
}
}
}Output
Name: Bala Age: 18 Year: 2018 Name: Rama Age: 17 Year: 2018 Name: Raju Age: 15 Year: 2018 Name: Raghav Age: 20 Year: 2018
Disadvantages of object arrays
- To store an object in an array often we need to know the length of the array often, which is not possible all the time.
- Once you create an object array you cannot modify its contents, there are no methods available to do so (unlike collections).
- It is not recommended to use array of objects (keeping memory issues in mind).