Sometimes, you may encounter interview questions like:
What are the methods of creating objects in Java?
In addition to new, what are the other ways to create objects in Java?
This article combines examples to give several Java methods to create objects. Here we go~~~~
Create with new
This is the most commonly used one. like:
Book book = new Book();
Examples are as follows:
package test;import java.io.Serializable;import java.util.List;/** * @author wangmengjun * */public class Book implements Serializable{ private static final long serialVersionUID = -6212470156629515269L; /**Book title*/ private String name; /**Author*/ private List<String> authors; /**ISBN*/ private String isbn; /**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. Create an object using new*/ 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);Use object.clone()
If you want to call the clone method, then 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; /**Book title*/ private String name; /**Author*/ private List<String> authors; /**ISBN*/ private String isbn; /**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(); }}Test code
/** * 1. Create an object using new*/ 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. Create an object using clone*/ try { Book book2 = (Book) book1.clone(); System.out.println(book2); } catch (CloneNotSupportedException e) { // TODO Auto-generated catch block e.printStackTrace(); }Use Class.newInstance()
It can be done 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(); }Use Contructor.newInstance()
You can specify a constructor to create, such as selecting the first constructor to create; you can also specify a constructor parameter type to create.
/** * 4. Use Constructor.newInstance(); */ try { //Select the first constructor to create Book Book book4 = (Book) Book.class.getConstructors()[0].newInstance(); //Book [name=null, authors=null, isbn=null, price=0.0] System.out.println(book4); /** * Call the specified constructor to create an 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(); }Using Class.newInstance() or Contructor.newInstance() is the same in essence, both adopt the reflection mechanism.
Using deserialization
/** * 5. Use 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, so I won’t list them one by one.
The complete example 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; /**Book title*/ private String name; /**Author*/ private List<String> authors; /**ISBN*/ private String isbn; /**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. Create an object using new*/ 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. Create an object using clone*/ 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 constructor to create Book Book book4 = (Book) Book.class.getConstructors()[0].newInstance(); //Book [name=null, authors=null, isbn=null, price=0.0] System.out.println(book4); /** * Call the specified constructor to create an 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=abc111111-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. Use 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(); } }}The above is all the content of this article. I hope it will be helpful to everyone's learning and I hope everyone will support Wulin.com more.