Java创建对象的几种方法

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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();    }

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转载于：https://my.oschina.net/wangmengjun/blog/790780

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