Java创建对象的几种方法
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2024-03-11 14:50:43
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，h...
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。