有時候，也可能碰到這樣面試題，如：
Java創建物件有哪幾種方法？
除了new之外，java建立物件還有哪幾種方式？
本文結合例子，給出幾種Java創建物件的方法，Here we go~~~~
使用new創建
這是最常用的一種。如：
Book book = new Book();
範例如下：
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()
如果要呼叫clone方法，那麼該object需要實作Cloneable介面，並重寫clone方法方法。
修改後的Book類別如下：
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();
}
}使用Class.newInstance()
可以直接使用Class.forName("xxx.xx").newInstance()方法或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()
可以指定建構器來創建，例如選擇第一個建構器創建；也可以指定建構子參數類型來建立。
/**
* 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Contructor.newInstance()，其本質是相同的，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。
完整的範例程式碼如下：
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; /**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();
}
}
}
