Java創建對象的幾種方法

有時候，也可能碰到這樣面試題，如：

Java創建對像有哪幾種方法？

除了new之外，java創建對像還有哪幾種方式？

本文結合例子，給出幾種Java創建對象的方法，Here we go~~~~

使用new創建

這是最常用的一種。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; /**書名*/ private String name; /**作者*/ private List<String> authors; /**ISBN*/ private String isbn; /**價格*/ 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創建對象*/ 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()

如果要調用clone方法，那麼該object需要實現Cloneable接口，並重寫clone()方法。

修改後的Book類如下：

 package test;import java.io.Serializable;import java.util.List;/** * @author wangmengjun * */public class Book implements Serializable, Cloneable { private static final long serialVersionUID = -6212470156629515269L; /**書名*/ private String name; /**作者*/ private List<String> authors; /**ISBN*/ private String isbn; /**價格*/ 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(); }}

測試代碼

 /** * 1. 使用new創建對象*/ 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創建對象*/ 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()

可以指定構造器來創建，如選擇第一個構造器創建；也可以指定構造函數參數類型來創建。

 /** * 4. 使用Constructor.newInstance(); */ try { //選擇第一個構造器創建Book Book book4 = (Book) Book.class.getConstructors()[0].newInstance(); //Book [name=null, authors=null, isbn=null, price=0.0] System.out.println(book4); /** * 調用指定構造函數創建對象*/ 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()，其本質是一樣的，都採用了反射機制。

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(); }

當然了，除了上述幾種方式之外，還可以使用JNI等方式來創建對象，這邊就不一一列舉了。

完整的示例代碼如下：

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; /**書名*/ private String name; /**作者*/ private List<String> authors; /**ISBN*/ private String isbn; /**價格*/ 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創建對象*/ 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創建對象*/ 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 { //選擇第一個構造器創建Book Book book4 = (Book) Book.class.getConstructors()[0].newInstance(); //Book [name=null, authors=null, isbn=null, price=0.0] System.out.println(book4); /** * 調用指定構造函數創建對象*/ 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內容，希望對大家的學習有所幫助，也希望大家多多支持武林網。