Java创建对象的几种方法
2024-08-29 16:53:29
有时候，也可能碰到这样面试题，如：
Java创建对象有哪几种方法？
除了new之外，java创建对象还有哪几种方式？
本文结合例子，给出几种Java创建对象的方法，Here we go~~~~
使用new创建
这是最常用的一种。如：
Book book = new Book();示例如下：
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);使用object.clone()
如果要调用clone方法，那么该object需要实现Cloneable接口，并重写clone()方法。
修改后的Book类如下：
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();
}
}
测试代码
/**
* 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();
}使用Class.newInstance()
可以直接使用Class.forName("xxx.xx").newInstance()方法或者XXX.class.newInstance()完成。
/**
* 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();
}使用Contructor.newInstance()
可以指定构造器来创建，如选择第一个构造器创建；也可以指定构造函数参数类型来创建。
/**
* 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();
}使用Class.newInstance()或者Contructor.newInstance()，其本质是一样的，都采用了反射机制。
使用反序列化
/**
* 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();
}当然了，除了上述几种方式之外，还可以使用JNI等方式来创建对象，这边就不一一列举了。
完整的示例代码如下：
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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