浅克隆(Shadow Clone):
把原型对象中成员变量为值类型的属性都复制给克隆对象,
把原型对象中成员变量为引用类型的引用地址也复制给克隆对象, 即 原型对象汇总如果有成员变量为引用对象,则此引用对象的地址是共享给原型对象的和克隆对象的
public class ShadowCloneTest {
public static void main(String[] args) throws Exception {
People p = new People(1,"哈哈");
People clone = (People) p.clone();
System.out.println(clone);
}
/**
* 1. 实现Cloneable 接口
* 2. 重写 clone 方法
*/
static class People implements Cloneable {
private Integer id;
private String name;
public People(Integer id, String name) {
this.id = id;
this.name = name;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "People{" +
"id=" + id +
", name='" + name + '\'' +
'}';
}
}
}
输出结果: People{id=1, name='哈哈'}
/**
* Creates and returns a copy of this object. The precise meaning
* of "copy" may depend on the class of the object. The general
* intent is that, for any object {@code x}, the expression:
* <blockquote>
* <pre>
* x.clone() != x</pre></blockquote>
* will be true, and that the expression:
* <blockquote>
* <pre>
* x.clone().getClass() == x.getClass()</pre></blockquote>
* will be {@code true}, but these are not absolute requirements.
* While it is typically the case that:
* <blockquote>
* <pre>
* x.clone().equals(x)</pre></blockquote>
* will be {@code true}, this is not an absolute requirement.
* <p>
* By convention, the returned object should be obtained by calling
* {@code super.clone}. If a class and all of its superclasses (except
* {@code Object}) obey this convention, it will be the case that
* {@code x.clone().getClass() == x.getClass()}.
* <p>
* By convention, the object returned by this method should be independent
* of this object (which is being cloned). To achieve this independence,
* it may be necessary to modify one or more fields of the object returned
* by {@code super.clone} before returning it. Typically, this means
* copying any mutable objects that comprise the internal "deep structure"
* of the object being cloned and replacing the references to these
* objects with references to the copies. If a class contains only
* primitive fields or references to immutable objects, then it is usually
* the case that no fields in the object returned by {@code super.clone}
* need to be modified.
* <p>
* The method {@code clone} for class {@code Object} performs a
* specific cloning operation. First, if the class of this object does
* not implement the interface {@code Cloneable}, then a
* {@code CloneNotSupportedException} is thrown. Note that all arrays
* are considered to implement the interface {@code Cloneable} and that
* the return type of the {@code clone} method of an array type {@code T[]}
* is {@code T[]} where T is any reference or primitive type.
* Otherwise, this method creates a new instance of the class of this
* object and initializes all its fields with exactly the contents of
* the corresponding fields of this object, as if by assignment; the
* contents of the fields are not themselves cloned. Thus, this method
* performs a "shallow copy" of this object, not a "deep copy" operation.
* <p>
* The class {@code Object} does not itself implement the interface
* {@code Cloneable}, so calling the {@code clone} method on an object
* whose class is {@code Object} will result in throwing an
* exception at run time.
*
* @return a clone of this instance.
* @throws CloneNotSupportedException if the object's class does not
* support the {@code Cloneable} interface. Subclasses
* that override the {@code clone} method can also
* throw this exception to indicate that an instance cannot
* be cloned.
* @see java.lang.Cloneable
*/
protected native Object clone() throws CloneNotSupportedException;
通过 Object#clone() 方法 源码可以知道:
1.对于所有对象来说, x.clone() != x 返回true,因为克隆对象和原对象不是同一个对象
2.对于所有对象来说,x.clone().getClass() == x.getClass() 返回true,因为克隆对象与原对象的类型是一样的
3.对于所有对象来说 ,x.clone().equals(x) 返回true,因为equals比较时,它们的值都相等
4. clone() 方法使用native修饰的本地方法,因此执行性能会很高,返回类型为Object,因此在调用克隆之后要把对象强转为目标类型才行
深克隆(Deep Clone):
将原型对象中的所有类型,无论是值类型还是引用类型,都复制一份给克隆对象, 即 深克隆会把原型对象和原型对象所引用的对象,都复制一份给克隆对象
实现深克隆的几种方式:
1.所有对象都实现克隆方法;
2.通过构造方法实现深克隆;
3.使用JDK自带的字节流实现深克隆;
4.使用第三方工具实现深克隆,比如ApacheCommonsLang;
5.使用JSON工具类实现;