浅谈Objeact.clone克隆(纯个人理解,如有错误请指正)

浅谈Objeact.clone克隆(纯个人理解,如有错误请指正)

现在先来看一下jdk给出的Object.clone源码和注释

    /**
     * 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:
     * 
*
     * x.clone() != x
* will be true, and that the expression: *
*
     * x.clone().getClass() == x.getClass()
* will be {
@code true}, but these are not absolute requirements. * While it is typically the case that: *
*
     * x.clone().equals(x)
* will be {
@code true}, this is not an absolute requirement. *

* 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()}. *

* 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. *

* 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. *

* 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;

克隆对象需要继承Cloneable接口并重写Object.clone()方法,看一下bean的代码

public class TestBean implements Cloneable{
    private Long id;
    private String code;
    private String msg;
    private TestCloneBean testCloneBean = new TestCloneBean();

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public TestCloneBean getTestCloneBean() {
        return testCloneBean;
    }

    public void setTestCloneBean(TestCloneBean testCloneBean) {
        this.testCloneBean = testCloneBean;
    }

    @Override
    protected TestBean clone() throws CloneNotSupportedException {
        return (TestBean)super.clone();
    }
}

克隆一个全新的对象,接下来看一下原本对象和新的克隆对象有什么区别

    public static void main(String[] args) {
        try {
            TestBean bean = new TestBean();
            TestBean copyBean = bean.clone();
            System.out.println("==判断:" + (bean == copyBean));
            System.out.println("class判断:" + (bean.getClass() == copyBean.getClass()));
            System.out.println("hasCode判断:" + (bean.hashCode() == copyBean.hashCode()));
            System.out.println("equals判断:" + (bean.equals(copyBean)));
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
    }

看一下结果

浅谈Objeact.clone克隆(纯个人理解,如有错误请指正)_第1张图片

除了.getClass()相等,其余皆是不一样的,是一个全新的对象。

-----------------------------------------------------------分割线-----------------------------------------------------------

那克隆对象里面包含对象呢?我们来看一下

public class Test {

    public static void main(String[] args) {
        try {
            TestBean bean = new TestBean();
            TestCloneBean testCloneBean = new TestCloneBean(1L,"1","测试");
            bean.setTestCloneBean(testCloneBean);
            TestBean copyBean = (TestBean) bean.clone();
            System.out.println("==判断:" + (bean.getTestCloneBean() == copyBean.getTestCloneBean()));
            System.out.println("class判断:" + (bean.getTestCloneBean().getClass() == copyBean.getTestCloneBean().getClass()));
            System.out.println("hasCode判断:" + (bean.getTestCloneBean().hashCode() == copyBean.getTestCloneBean().hashCode()));
            System.out.println("equals判断:" + (bean.getTestCloneBean().equals(copyBean.getTestCloneBean())));
            System.out.println("bean:{"+bean.getTestCloneBean().toString()+"}");
            System.out.println("bean:{"+copyBean.getTestCloneBean().toString()+"}");
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
    }
}

#1 属性testCloneBean未重写clone方法,结果是

浅谈Objeact.clone克隆(纯个人理解,如有错误请指正)_第2张图片

#2 当对象属性也重写了clone方法后

    @Override
    public TestCloneBean clone() throws CloneNotSupportedException {
        return (TestCloneBean) super.clone();
    }

结果是

浅谈Objeact.clone克隆(纯个人理解,如有错误请指正)_第3张图片

很诧异,还是原来的地址,说明对象属性是没有被克隆的,那是不是对象没有序列化呢?等我加上序列化试一下

额~事实证明,序列化还是一样的,被克隆的对象属性是一样的!

posted @ 2018-08-03 21:21 dawn-tangzedong 阅读( ...) 评论( ...) 编辑 收藏

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