Manchmal stoßen Sie möglicherweise auch auf solche Interviewfragen, wie zum Beispiel:
Wie können Objekte in Java erstellt werden?
Welche anderen Möglichkeiten gibt es außer den neuen Möglichkeiten, Objekte in Java zu erstellen?
Dieser Artikel kombiniert Beispiele, um verschiedene Methoden zum Erstellen von Objekten in Java aufzuzeigen~~~~
Verwenden Sie „New“, um zu erstellen
Dies ist die am häufigsten verwendete Methode . Zum Beispiel:
Book book = new Book();
Das Beispiel sieht wie folgt aus:
package test;
import java.io.Serializable;
import java.util.List;
/**
* @author wangmengjun
*
*/
public class Book implements Serializable{
private static final long serialVersionUID = -6212470156629515269L;
/**书名*/
private String name;
/**作者*/
private List<String> authors;
/**ISBN*/
private String isbn;
/**价格*/
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. 使用new创建对象
*/
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()
Wenn Sie die Methode clone aufrufen möchten, muss das Objekt die Schnittstelle Cloneable implementieren und die Methode clone() überschreiben.
Die geänderte Buchklasse lautet wie folgt:
package test;import java.io.Serializable;import java.util.List;/**
* @author wangmengjun
*
*/public class Book implements Serializable, Cloneable { private static final long serialVersionUID = -6212470156629515269L; /**书名*/
private String name; /**作者*/
private List<String> authors; /**ISBN*/
private String isbn; /**价格*/
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();
}
}Verwenden Sie Class.newInstance()
Sie können Class.forName("xxx.xx") direkt verwenden. Die Methode newInstance( ) oder XXX.class.newInstance() ist abgeschlossen.
/**
* 3. 使用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();
}Mit Contructor.newInstance()
können Sie einen zu erstellenden Konstruktor angeben, z. B. den ersten zu erstellenden Konstruktor auswählen; Sie können auch den zu erstellenden Konstruktorparametertyp angeben.
/**
* 4. 使用Constructor.newInstance();
*/
try { //选择第一个构造器创建Book
Book book4 = (Book) Book.class.getConstructors()[0].newInstance(); //Book [name=null, authors=null, isbn=null, price=0.0]
System.out.println(book4); /**
* 调用指定构造函数创建对象
*/
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();
}Verwenden Sie Class.newInstance() oder Constructor.newInstance(). Das Wesentliche ist dasselbe, beide verwenden den Reflexionsmechanismus.
Deserialisierung verwenden
/**
* 5. 使用反序列化
*/
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();
}Zusätzlich zu den oben genannten Methoden können Sie natürlich auch JNI und andere Methoden zum Erstellen von Objekten verwenden, die hier nicht aufgeführt werden.
Der vollständige Beispielcode lautet wie folgt:
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; /**书名*/
private String name; /**作者*/
private List<String> authors; /**ISBN*/
private String isbn; /**价格*/
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. 使用new创建对象
*/
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. 使用clone创建对象
*/
try {
Book book2 = (Book) book1.clone();
System.out.println(book2);
} catch (CloneNotSupportedException e) { // TODO Auto-generated catch block
e.printStackTrace();
} /**
* 3. 使用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. 使用Constructor.newInstance();
*/
try { //选择第一个构造器创建Book
Book book4 = (Book) Book.class.getConstructors()[0].newInstance(); //Book [name=null, authors=null, isbn=null, price=0.0]
System.out.println(book4); /**
* 调用指定构造函数创建对象
*/
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. 使用反序列化
*/
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();
}
}
}
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