有时候,也可能碰到这样面试题,如:
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:
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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 + "]" ; } } |
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/** * 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:
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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
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/** * 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。
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/** * 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。
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/** * 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
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/** * 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
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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
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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(); } } } |
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。