Java创建对象的几种方法

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();
    }
  }

}

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。