Java several ways to create objects
- 2020-05-24 05:33:29
- OfStack
Sometimes, you may come across such interview questions, such as:
How many ways can Java create objects?
In addition to new, what other ways can java create objects?
In this paper, several methods of creating objects by Java are given with examples, Here we go~~~~ ~
Create using new
This is the most common one. Such as:
Book book = new Book();
Here's an example:
package test;
import java.io.Serializable;
import java.util.List;
/**
* @author wangmengjun
*
*/
public class Book implements Serializable{
private static final long serialVersionUID = -6212470156629515269L;
/** Title: */
private String name;
/** The author */
private List<String> authors;
/**ISBN*/
private String isbn;
/** The price */
private float price;
public Book() {
}
/**
* @param name
* @param authors
* @param isbn
* @param price
*/
public Book(String name, List<String> authors, String isbn, float price) {
this.name = name;
this.authors = authors;
this.isbn = isbn;
this.price = price;
}
/**
* @return the name
*/
public String getName() {
return name;
}
/**
* @param name the name to set
*/
public void setName(String name) {
this.name = name;
}
/**
* @return the authors
*/
public List<String> getAuthors() {
return authors;
}
/**
* @param authors the authors to set
*/
public void setAuthors(List<String> authors) {
this.authors = authors;
}
/**
* @return the isbn
*/
public String getIsbn() {
return isbn;
}
/**
* @param isbn the isbn to set
*/
public void setIsbn(String isbn) {
this.isbn = isbn;
}
/**
* @return the price
*/
public float getPrice() {
return price;
}
/**
* @param price the price to set
*/
public void setPrice(float price) {
this.price = price;
}
/* (non-Javadoc)
* @see java.lang.Object#toString()
*/
@Override
public String toString() {
return "Book [name=" + name + ", authors=" + authors + ", isbn=" + isbn + ", price="
+ price + "]";
}
}
/**
* 1. use new Create an object
*/
Book book1 = new Book();
book1.setName("Redis");
book1.setAuthors(Arrays.asList("Eric", "John"));
book1.setPrice(59.00f);
book1.setIsbn("ABBBB-QQ677868686-HSDKHFKHKH-2324234");
System.out.println(book1);
Using object. clone ()
If you want to call the clone method, the object needs to implement the Cloneable interface and override the clone() method.
The modified Book class is as follows:
package test;
import java.io.Serializable;
import java.util.List;
/**
* @author wangmengjun
*
*/
public class Book implements Serializable, Cloneable {
private static final long serialVersionUID = -6212470156629515269L;
/** Title: */
private String name;
/** The author */
private List<String> authors;
/**ISBN*/
private String isbn;
/** The price */
private float price;
public Book() {
}
/**
* @param name
* @param authors
* @param isbn
* @param price
*/
public Book(String name, List<String> authors, String isbn, float price) {
this.name = name;
this.authors = authors;
this.isbn = isbn;
this.price = price;
}
/**
* @return the name
*/
public String getName() {
return name;
}
/**
* @param name the name to set
*/
public void setName(String name) {
this.name = name;
}
/**
* @return the authors
*/
public List<String> getAuthors() {
return authors;
}
/**
* @param authors the authors to set
*/
public void setAuthors(List<String> authors) {
this.authors = authors;
}
/**
* @return the isbn
*/
public String getIsbn() {
return isbn;
}
/**
* @param isbn the isbn to set
*/
public void setIsbn(String isbn) {
this.isbn = isbn;
}
/**
* @return the price
*/
public float getPrice() {
return price;
}
/**
* @param price the price to set
*/
public void setPrice(float price) {
this.price = price;
}
/* (non-Javadoc)
* @see java.lang.Object#toString()
*/
@Override
public String toString() {
return "Book [name=" + name + ", authors=" + authors + ", isbn=" + isbn + ", price="
+ price + "]";
}
@Override
protected Object clone() throws CloneNotSupportedException {
return (Book) super.clone();
}
}
The test code
/**
* 1. use new Create an object
*/
Book book1 = new Book();
book1.setName("Redis");
book1.setAuthors(Arrays.asList("Eric", "John"));
book1.setPrice(59.00f);
book1.setIsbn("ABBBB-QQ677868686-HSDKHFKHKH-2324234");
System.out.println(book1);
/**
* 2. use clone Create an object
*/
try {
Book book2 = (Book) book1.clone();
System.out.println(book2);
} catch (CloneNotSupportedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Using Class. newInstance ()
You can do this directly using the Class.forName (" xxx.xx ").newInstance () method or XXX.class.newInstance ().
/**
* 3. use Class.newInstance();
*/
try {
Book book3 = (Book) Class.forName("test.Book").newInstance();
System.out.println(book3);
book3 = Book.class.newInstance();
System.out.println(book3);
} catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Using Contructor. newInstance ()
You can specify a constructor to create, such as selecting the first constructor to create. You can also specify the constructor parameter type to create.
/**
* 4. use Constructor.newInstance();
*/
try {
// Select the first 1 Constructors are created Book
Book book4 = (Book) Book.class.getConstructors()[0].newInstance();
//Book [name=null, authors=null, isbn=null, price=0.0]
System.out.println(book4);
/**
* Calls the specified constructor to create the object
*/
book4 = (Book) Book.class.getConstructor(String.class, List.class, String.class,
float.class).newInstance("New Instance Example", Arrays.asList("Wang", "Eric"),
"abc1111111-def-33333", 60.00f);
//Book [name=New Instance Example, authors=[Wang, Eric], isbn=abc1111111-def-33333, price=60.0]
System.out.println(book4);
} catch (InstantiationException | IllegalAccessException | IllegalArgumentException
| InvocationTargetException | SecurityException | NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Use Class.newInstance () or Contructor.newInstance (), which are essentially 1, using reflection.
Using deserialization
/**
* 5. Using deserialization
*/
try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("book.dat"));
ObjectInputStream ois = new ObjectInputStream(new FileInputStream("book.dat"));) {
oos.writeObject(book1);
Book book5 = (Book) ois.readObject();
System.out.println(book5);
} catch (IOException | ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Of course, in addition to the above methods, you can also use JNI and other methods to create objects, which is not listed here.
The complete sample code is as follows:
Book.java
package test;
import java.io.Serializable;
import java.util.List;
/**
* @author wangmengjun
*
*/
public class Book implements Serializable, Cloneable {
private static final long serialVersionUID = -6212470156629515269L;
/** Title: */
private String name;
/** The author */
private List<String> authors;
/**ISBN*/
private String isbn;
/** The price */
private float price;
public Book() {
}
/**
* @param name
* @param authors
* @param isbn
* @param price
*/
public Book(String name, List<String> authors, String isbn, float price) {
this.name = name;
this.authors = authors;
this.isbn = isbn;
this.price = price;
}
/**
* @return the name
*/
public String getName() {
return name;
}
/**
* @param name the name to set
*/
public void setName(String name) {
this.name = name;
}
/**
* @return the authors
*/
public List<String> getAuthors() {
return authors;
}
/**
* @param authors the authors to set
*/
public void setAuthors(List<String> authors) {
this.authors = authors;
}
/**
* @return the isbn
*/
public String getIsbn() {
return isbn;
}
/**
* @param isbn the isbn to set
*/
public void setIsbn(String isbn) {
this.isbn = isbn;
}
/**
* @return the price
*/
public float getPrice() {
return price;
}
/**
* @param price the price to set
*/
public void setPrice(float price) {
this.price = price;
}
/* (non-Javadoc)
* @see java.lang.Object#toString()
*/
@Override
public String toString() {
return "Book [name=" + name + ", authors=" + authors + ", isbn=" + isbn + ", price="
+ price + "]";
}
@Override
protected Object clone() throws CloneNotSupportedException {
return (Book) super.clone();
}
}
CreateObjectExample.java
package test;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.InvocationTargetException;
import java.util.Arrays;
import java.util.List;
/**
* @author wangmengjun
*
*/
public class CreateObjectExample {
public static void main(String[] args) {
/**
* 1. use new Create an object
*/
Book book1 = new Book();
book1.setName("Redis");
book1.setAuthors(Arrays.asList("Eric", "John"));
book1.setPrice(59.00f);
book1.setIsbn("ABBBB-QQ677868686-HSDKHFKHKH-2324234");
System.out.println(book1);
/**
* 2. use clone Create an object
*/
try {
Book book2 = (Book) book1.clone();
System.out.println(book2);
} catch (CloneNotSupportedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
/**
* 3. use Class.newInstance();
*/
try {
Book book3 = (Book) Class.forName("test.Book").newInstance();
System.out.println(book3);
book3 = Book.class.newInstance();
System.out.println(book3);
} catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
/**
* 4. use Constructor.newInstance();
*/
try {
// Select the first 1 Constructors are created Book
Book book4 = (Book) Book.class.getConstructors()[0].newInstance();
//Book [name=null, authors=null, isbn=null, price=0.0]
System.out.println(book4);
/**
* Calls the specified constructor to create the object
*/
book4 = (Book) Book.class.getConstructor(String.class, List.class, String.class,
float.class).newInstance("New Instance Example", Arrays.asList("Wang", "Eric"),
"abc1111111-def-33333", 60.00f);
//Book [name=New Instance Example, authors=[Wang, Eric], isbn=abc1111111-def-33333, price=60.0]
System.out.println(book4);
} catch (InstantiationException | IllegalAccessException | IllegalArgumentException
| InvocationTargetException | SecurityException | NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
/**
* 5. Using deserialization
*/
try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("book.dat"));
ObjectInputStream ois = new ObjectInputStream(new FileInputStream("book.dat"));) {
oos.writeObject(book1);
Book book5 = (Book) ois.readObject();
System.out.println(book5);
} catch (IOException | ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}