initialize object directly in java

Question

Is that possible to initialize object directly as we can do with String class in java:

such as:

String str="something...";

I want to do same for my custom class:

class MyData{
public String name;
public int age;
}

is that possible like

MyClass obj1={"name",24};

or

MyClass obj1="name",24;

to initialize object? or how it can be possible!

Answer 1

Normally, you would use a constructor, but you don't have to!

Here's the constructor version:

public class MyData {
    private String name;
    private int age;

    public MyData(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // getter/setter methods for your fields
}

which is used like this:

MyData myData = new MyData("foo", 10);

However, if your fields are protected or public, as in your example, you can do it without defining a constructor. This is the closest way in java to what you want:

// Adding special code for pedants showing the class without a constuctor
public class MyData {
    public String name;
    public int age;
}

// this is an "anonymous class"
MyData myData = new MyData() {
    {
        // this is an "initializer block", which executes on construction
        name = "foo";
        age = 10;
    }
};

Voila!

Answer 2

If you have a class Person:

public class Person {

    private String lastName;
    private String firstName;

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

}

You can actually create a new Person object and initialize its firstName and lastName with the following:

 Person person = new Person(){{
     setFirstName("My FirstName");
     setLastName("MyLastName");
 }}

This is used quite often when defining Spring Configuration using Java code instead of XML configuration.

Answer 3

You have to make a constructor method for the object, which takes in parameters of the fields you want values for.

Example:

public myClass( int age, String name)
{
   this.age = age;
   this.name = name;
}

Then in the class you want this:

myClass class = new myClass(24, "name");

Answer 4

I know that with constructors, but any alternative way is present or not?

No, there are no alternatives to constructors.

That's basically one of the fundamental guarantees of the language. An object can't be constructed by any other means than through its constructors and there's no alternative syntax then the usual new ConstructorName(...).

The closest idea I can come up with would be to have a static factory method called say, mc:

class MyClass {
    ...
    public static mc(String name, int age) {
        return new MyClass(name, age);
    }
}

and then do

import static some.pkg.MyClass.mc;

...

MyClass obj1 = mc("name",24);

Answer 5

It is possible with the keyword new and using constructors, but not like the String, that is a very special kind of object.

Answer 6

class MyData{

    public MyData(String name, int age) {
        this.name = name;
        this.age = age;
    }
    public String name;
    public int age;
    }

Then you can instantiate your class this way:

MyData myData = new MyData("name", 24);

Answer 7

    package com.company;

public class InitializationOfObject {
    int a ;
    int b ;

    InitializationOfObject(){
    }

    InitializationOfObject( int r , int n){
        this.a = r;
        this.b = n;
        System.out.println("Object initialization by constructor  ");
    }

    void methodInitialization(int k, int m){
        System.out.println("object initialization via method");
        this.a = k;
        this.b = m;
    }

    void display(){
        System.out.println("k = " +a+ "m = "+b);
    }

    public static void main(String... arg){
        InitializationOfObject io = new InitializationOfObject();
        InitializationOfObject io2 = new InitializationOfObject(45,65);
        io.a = io2.a;
        io.b = io2.b;
        io.display();

        io.methodInitialization(34,56);
        io.display();

        io.a = 12;
        io.b = 24;
        System.out.println("object initialization via refrence");
        System.out.println("a = "+io.a+" "+ " b ="+io.b);
    }

}

//Object initializatian by construtor

k = 45m = 65

object initializaion via method

k = 34m = 56

object initialization via reference

a = 12  b =24

Answer 8

There are two types of Constructors in java.

1. Default constructor
2. Parameterized constructor

You should create a parameterized constructor to create your object.

Answer 9

The following does what you want, but not in the way that you would expect.

So in a class calling MyData, you would use

Public MyData x = new MyData();
@PostConstruct public void init() {
     x.setName("Fering");
     x.setAge(18);
}

So once the object is construsted, these commands are run, which allows you to populate the object before anything else runs.

So with this you do not have to use anonymous subclasses, or create new constructors, you can just take the class and then use its functions, before anything else would.

Answer 10

There is no alternative to constructors (along with new operator) in java during the object initialization. You have mentioned as

String str = "something"

you can initialize string that way, because String is a literal in java. Only literals can initialized that way. A a composite object can not initialized, but only can be instantiated with the new operator with the constructors.