浅谈Objeact.clone克隆

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:
     * <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;

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

除了.getClass()相等，其余皆是不一样的，是一个全新的对象。

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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

#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

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！