Java Constructor vs method

By Sidd Bhattacharjee -
Functionally difference between constructors and methods is that constructors create and initialize objects that don't exist yet, while methods perform operations on objects that already exist.

Constructors can't be called directly. They are invoked implicitly when the new keyword creates an object.
Methods can be called directly on an object that has already been created with new.

Constructors must be named with the same name as the class name.

Constructors cannot  return anything, even void .

Methods must be declared to return something ( or void).

Constructor compiler provide default constructor where as method compiler does't provide.

Constructor cannot be final since it cant be inherited.

Constructor cannot be abstract since it is used to create and initialize object.

Constructor cannot be static since it is used to create instance of object.

Only public, protected & private modifiers are permitted.

Comments

Post a Comment

Popular posts from this blog

Converting Java Map to String

By -
Java Collections framework, String manipulation etc is something that we often encounter in Development process. For processing collections (like checking null/empty, Intersection, Disjunction) We do have some of the very use full libraries. Some of the Collection related libraries are Apche Commons Collections and Google  Collections(Guava). Problem Use Case This article explains how to convert a Java Map to String(and vice versa) using different libraries and technique. One way is to use StringBuilder(Or String) and loop though the Map and build the String by applying some sort of separator ( for key:value and entry). Here we have to take care of the null value etc. Without Any Library If we want to convert the map to a String with key value separator and also individual entry seperator in the resulting String, we have to write code for that. For a simple Map, we have to iterate though the map, take care of the null values etc. Following is a sample to get String built
Read more

Difference between volatile and synchronized

By -
volatile is a field modifier, while synchronized modifies code blocks and methods. So we can specify three variations of a simple accessor using those two keywords: int i1; int geti1() {return i1;} volatile int i2; int geti2() {return i2;} int i3; synchronized int geti3() {return i3;} geti1() accesses the value currently stored in i1 in the current thread . Threads can have local copies of variables, and the data does not have to be the same as the data held in other threads. In particular, another thread may have updated i1 in it's thread, but the value in the current thread could be different from that updated value. In fact Java has the idea of a "main" memory, and this is the memory that holds the current "correct" value for variables. Threads can have their own copy of data for variables, and the thread copy can be different from the "main" memory. So in fact, it is possible for the "main"
Read more

Invoking EJB deployed on a remote machine

By -
Invoking EJB deployed on a remote machine In case we are calling remote ejb( ejb deployed on remote machines), The JNDI lookup might lookup like, Properties env = new Properties(); env.put(Context.INITIAL_CONTEXT_FACTORY, "org.jnp.interfaces.NamingContextFactory"); env.put(Context.PROVIDER_URL, "XX.XXX.XX.XX:1099"); env.put("java.naming.factory.url.pkgs", "org.jboss.naming:org.jnp.interfaces"); Context ctx = new InitialContext(env); If we are calling local ejb then we can simply create InitialContext without any parameters. Like, Context ctx = new InitialContext();
Read more