Why Do We Need Constructor With Arguments?

Question

I understand that constructor is used to create instances.
We can have constructors with 0 argument or with one/multiple arguments. Why do we need a contructor with arguments? What is the purpose of doing it?
Thank you for your help.

Answer 1

There are three general ways to provide constructors, like you said:
1) Default constructor (no arguments)
2) One or more constructors with arguments
3) One or more constructors with arguments as well as a default constructor
From a design standpoint, the idea is to give as much information needed for constructing an object up front. Look at the standard Java API for some examples (and because I couldn't find a standard class with just a default constructor, one made up):
public class Foo {
  private long createTime;
  public Foo() {
    createTime = System.currentTimeMillis();
  public String toString() {
    return "This object was created at " + createTime;
}This code has no reason to take any arguments. It does all construction on its own and already has all the information it needs. On the other hand, look at BufferedReader. There's no possible way this object can ever be constructed without an argument. What's it buffering? It doesn't make sense to ever instantiate new BufferedReader(). It'd be useless. So BufferedReader has no default (no-arg) constructor.
Sometimes (very often in Java) you want to do both. Let something be instantiated with no arguments, but also provide the option of creating something with more specific details. A good example is ArrayList, which has three constructors:
public ArrayList() --> Construct an empty ArrayList with the default initial capacity;
public ArrayList(Collection c) --> Construct an ArrayList populated with the contents of another collection;
public ArrayList(int capacity) --> Construct an empty ArrayList with a specific initial capacity.
Sometimes it makes sense just to use the default. Sometimes you want more control over the behavior. Those are the times to use multiple constructors.
Hope this helps!