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。
