Java what is new keyword

Содержание

Java new Keyword
Java new Keyword
Syntax
Points to remember
Examples of Java new Keyword
Example 1
Example 2
Example 3
Example 4
Example 5
What is java new? A function or keyword
Creating objects with «new» keyword or without «new» in Java
Java- Creating String object using new keyword
What is new Keyword in Java
How to use the new keyword?
Java new Keyword Example
Example 2: Calling parameterized constructor to create object
Example 3: new keyword with array
Example 4: new keyword with strings
Example 5: Creating an object of a collection class
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Java new Keyword

When we create String object using new keyword as In this case, we are passing a argument of String type. This allows creation of inner classes — non-static nested classes that hold an implicit reference to an instance of the outer class.

Java new Keyword

The Java new keyword is used to create an instance of the class. In other words, it instantiates a class by allocating memory for a new object and returning a reference to that memory. We can also use the new keyword to create the array object.

Syntax

NewExample obj=new NewExample();

Points to remember

It is used to create the object.
It allocates the memory at runtime.
All objects occupy memory in the heap area.
It invokes the object constructor.
It requires a single, postfix argument to call the constructor

Examples of Java new Keyword

Example 1

Let’s see a simple example to create an object using new keyword and invoking the method using the corresponding object reference.

public class NewExample1 public static void main(String[] args) < NewExample1 obj=new NewExample1(); obj.display(); >>

Example 2

Let’s see a simple example to create an object using new keyword and invoking the constructor using the corresponding object reference.

public class NewExample2 public static void main(String[] args) < NewExample2 obj=new NewExample2();>>

Example 3

Here, we create an object using new keyword and invoke the parameterized constructor.

public class NewExample3 void display() < System.out.println(a+b); >public static void main(String[] args) < NewExample3 obj=new NewExample3(10,20); obj.display(); >>

Example 4

Let’s see an example to create an array object using the new keyword.

Example 5

Let’s see an example to use new keywords in Java collections.

import java.util.*;public class NewExample5 >

Java — Why new keyword not needed for String, Actually, you can not create any object in Java without using the keyword new. e.g. Integer i = 1; Does, not mean that the Integer object is …

What is java new? A function or keyword

As i understand new is a keyword and not a function.

instantiates the object a of type A.
A keyword is not associated with any object per se.

On the contrary, when we have in A a public inner class B we call

Here it looks like new is a property of B and not an independent keyword.

What is the meaning of A.new ?

New is a keyword in both cases. It’s part of a class instance creation expression .

There are two forms: unqualified and qualified .

The unqualified form starts with the keyword ‘new’.

The qualified form starts with a primary class, then ‘new’. This allows creation of inner classes — non-static nested classes that hold an implicit reference to an instance of the outer class. The qualified form provides a way to specify that instance.

From the Java Language Specification, section 15.9:

Unqualified class instance creation expressions begin with the keyword new.

An Unqualified class instance creation expression may be used to create an instance of a class, regardless of whether the class is a top level (§7.6), member (§8.5, §9.5), local (§14.3) or anonymous class (§15.9.5).

Qualified class instance creation expressions begin with a Primary.

A qualified class instance creation expression enables the creation of instances of inner member classes and their anonymous subclasses.

new is a keyword which has it’s own syntax (as you have noticed). See JLS 3.9

Java doesn’t have functions as such. It has methods and Java 8 will add more functional features.

It would be B b = a.new B(); and new is still just a keyword. The reference to the object a shows the compiler that B is a nested class. http://docs.oracle.com/javase/tutorial/java/javaOO/nested.html

B b = A.new B(); // A should be an instance object not a class name, // otherwise it's not a valid syntax

You are creating an object of type B that would have access to instance members of the instance A .

Java memory questions about ‘new’ keyword, In theory, new creates on the Heap, and non-objects (i.e., ints, chars and so on) are created on the stack.The only exception, afaik, are strings, …

Creating objects with «new» keyword or without «new» in Java

Hi there i am working on LinkedList project with Java and i have some unclear issues in my mind. for example this is my «Patient» class;

and when i construct my LinkedList i create a header and tail node like this.

private Patient header = new Patient(0, null, null, null, null, null); private Patient tail = new Patient(0, null, null ,null ,null, null);

but if i create these two nodes without new Patient(0, null, null, null, null, null); anything doesnt change. could you please explain why_?

You get null references when not using the new keyword. Have you tried to access and do something with Objects that aren’t instanced with the new key word? Add a method called getName() and call it on a Patient variable before it is instanced. This will result in an «null pointer exception»

Java — When is the appropriate time to use the ‘new’, You use the new keyword when an object is being explicitly created for the first time. Then fetching an object using a getter method new is not required …

Java- Creating String object using new keyword

I know the difference between string literal and new String object and also know how it works internally.But my question is little bit advance of this.When we create string object using new keyword as

String str = new String("test");

In this case, we are passing a argument of String type. My questions is where this string gets generated — Heap Or String constant pool Or somewhere else?

As up to my knowledge, this argument is a string literal so it should be in string constant pool.If is it so then what is use of intern method — only just link variable str to constant pool? because «test» would be available already.

Please clarify me, if I had misunderstood the concept.

The statement String str = new String(«test»); creates a string object which gets stored on the heap like any other object. The string literal «test» that is passed as an argument is stored in the String Constant Pool.

String#intern() checks if a string constant is already available in the string pool. If there is one already it returns it, else it creates a new one and stores it in the pool. See the Javadocs:

Returns a canonical representation for the string object.

A pool of strings, initially empty, is maintained privately by the class String .

When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the equals(Object) method, then the string from the pool is returned. Otherwise, this String object is added to the pool and a reference to this String object is returned.

It follows that for any two strings s and t , s.intern() == t.intern() is true if and only if s.equals(t) is true.

Starting from JDK7, interned strings are stored on the heap. This is from the release notes of JDK7:

In JDK 7, interned strings are no longer allocated in the permanent generation of the Java heap, but are instead allocated in the main part of the Java heap (known as the young and old generations), along with the other objects created by the application. This change will result in more data residing in the main Java heap, and less data in the permanent generation, and thus may require heap sizes to be adjusted. Most applications will see only relatively small differences in heap usage due to this change, but larger applications that load many classes or make heavy use of the String.intern() method will see more significant differences.

public static void main(String[] args) throws IOException < String s = new String(new char[] < 'a', 'b', 'c' >); // "abc" will not be added to String constants pool. System.out.println(System.identityHashCode(s)); s = s.intern();// add s to String constants pool System.out.println(System.identityHashCode(s)); String str1 = new String("hello"); String str2 = "hello"; String str3 = str1.intern(); System.out.println(System.identityHashCode(str1)); System.out.println(System.identityHashCode(str2)); System.out.println(System.identityHashCode(str3)); >

1414159026 1569228633 --> OOPs String moved to String constants pool 778966024 1021653256 1021653256 --> "hello" already added to string pool. So intern does not add it again.

What does the ‘new’ keyword actually do in Java, and, The new keyword does exactly what it says on the tin, it creates a brand new object, irrespective of whether one already exists. It creates a new object and …

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What is new Keyword in Java

The new keyword is used to create an object of a class.

It allocates a memory to the object during runtime.
It invokes the specified constructor of the class to create the object.
It returns a reference to the allocated memory.

How to use the new keyword?

The following syntax is used to create an instance (object) of the class.

ClassName objectName = new ClassName();

// This statement will create the object of the // String class and the returned reference is // assigned to the object str. String str = new String();

Java new Keyword Example

Here, we have a class JavaExample , which contains a variable and a method. In order to access the variable and method, we need to create an object of this class. In this example, we have created an object obj of this class using new keyword.

public class JavaExample < int num = 100; //variable public void demo()< System.out.println("hello"); >public static void main(String[] args) < JavaExample obj = new JavaExample(); System.out.println(obj.num); obj.demo(); >>

In the above example, we have used the following statement to create the object.

JavaExample obj = new JavaExample();

This object creation can be divided into three parts:

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Declaration: Class name followed by object name. This creates a reference of the class.

Instantiation: new keyword followed by the constructor of the class. This creates an object of the class, whose constructor is being called.

Initialization: Initializing the reference of class with the created object.

JavaExample obj = new JavaExample();

Example 2: Calling parameterized constructor to create object

In the above example, the new keyword calls the default constructor of the class, which is by default created for the each class. However if a class has a constructor that accepts arguments then we can pass the arguments while creating an instance of the class using new keyword.

public class JavaExample < String myName; int myAge; JavaExample(String name, int age)< myName = name; myAge = age; >public static void main(String[] args) < JavaExample person = new JavaExample("Chaitanya", 35); //Accessing the parameters of the created instance System.out.println(person.myName); System.out.println(person.myAge); >>

Example 3: new keyword with array

Here, we are using the new keyword to create an array object.

Example 4: new keyword with strings

We can also create an object of String class using new keyword. There is a difference between simple assignment and assignment using new, the difference is covered in Java String Tutorial.

Example 5: Creating an object of a collection class

We can also use new keyword to create object of various collection classes. In the following example, we are creating an object of ArrayList class.

import java.util.ArrayList; public class JavaExample < public static void main(String[] args) < ArrayListarrList = new ArrayList<>(); arrList.add(101); arrList.add(201); arrList.add(301); arrList.add(401); for(int i: arrList) < System.out.println(i); >> >

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