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Java中的深克隆和浅克隆——Cloneable接口
一、没有使用克隆带来的问题
public class CloneTest
{
static Student s = new Student("aaa", 20);
// 直接赋值带来的问题
public static void noclone()
{
// 传的是引用的副本，改变了noCloneStudent也改变了s
Student noCloneStudent = new Student();
noCloneStudent = s;
noCloneStudent.setName("bbb");
noCloneStudent.setAge(21);
System.out.println(s);
System.out.print(noCloneStudent);
}
}
Student [name=bbb, age=21]
Student [name=bbb, age=21]
本意是设置noCloneStudent中的值，但把原来的对象s中的值也改变了。
二、浅克隆与深克隆
①浅克隆——若要克隆Student对象，只克隆他自身以及他包含的所有对象的引用地址。
②深克隆——克隆除自身以外所有的对象，包括自身所包含的所有对象实例。由具体的需求决定深克隆的层次(N层克隆)。
三、浅克隆
public class Student implements Cloneable
{
private String name;
private int age;
public Student()
{
super();
}
public Student(String name, int age)
{
super();
this.name = name;
this.age = age;
}
// 浅克隆
protected Object clone() throws CloneNotSupportedException
{
return super.clone();
}
public String toString()
{
return "Student [name=" + name + ", age=" + age + "]";
}
......
}
public class CloneTest
{
static Student s = new Student("aaa", 20);
// 浅克隆
public static void test0() throws Exception
{
Student ss = (Student) s.clone();
ss.setName("bbb");
ss.setAge(21);
System.out.println(s);
System.out.print(ss);
}
}
Student [name=aaa, age=20]
Student [name=bbb, age=21]
克隆的效果就达到了。
四、深克隆
public class TClass implements Cloneable
{
private Student stu;
private String name;
private List<String> courses = new ArrayList<String>();
public TClass()
{
super();
}
public TClass(Student stu, String name, List<String> courses)
{
super();
this.stu = stu;
this.name = name;
this.courses = courses;
}
// 深克隆
public Object clone() throws CloneNotSupportedException
{
TClass tea = (TClass) super.clone();
tea.stu = (Student) tea.stu.clone();
return tea;
}
public String toString()
{
return "TClass [stu=" + stu + ", name=" + name + ", courses=" + courses + "]";
}
......
}
// 深克隆
public static void test1() throws Exception
{
TClass t = new TClass();
t.setStu(s);
t.setName("张老师");
t.getCourses().add("JAVA");
t.getCourses().add("C#");
System.out.println(t);
TClass tt = (TClass) t.clone();
Student sss = (Student) s.clone();
sss.setName("bbb");
sss.setAge(21);
tt.setStu(sss);
tt.setName("李老师");
tt.getCourses().add("oracle");
tt.getCourses().add("mysql");
System.out.println(t);
System.out.println(tt);
}
TClass [stu=Student [name=aaa, age=20], name=张老师, courses=[JAVA, C#]]
TClass [stu=Student [name=aaa, age=20], name=张老师, courses=[JAVA, C#, oracle, mysql]]
TClass [stu=Student [name=bbb, age=21], name=李老师, courses=[JAVA, C#, oracle, mysql]]
动态数组还是保留了原来的引用，所以其数组没有达到拷贝的效果。
改造一下，让其中的数组有新的引用
public class TClass implements Cloneable
{
private Student stu;
private String name;
private List<String> courses = new ArrayList<String>();
public TClass()
{
super();
}
public TClass(Student stu, String name, List<String> courses)
{
super();
this.stu = stu;
this.name = name;
this.courses = courses;
}
// 深克隆(更深一层)
public Object clone() throws CloneNotSupportedException
{
TClass tea = (TClass) super.clone();
tea.stu = (Student) tea.stu.clone();
tea.courses = new ArrayList<String>(); // 指向不同引用
return tea;
}
public String toString()
{
return "TClass [stu=" + stu + ", name=" + name + ", courses=" + courses + "]";
}
......
}
TClass[stu=Student [name=aaa, age=20], name=张老师, courses=[Java, C#]]
TClass[stu=Student [name=bbb, age=21], name=李老师, courses=[oracle, mysql]]
再改造一下，希望动态数组既有了新的引用，又保留了原值
public class TClass3 implements Cloneable
{
private Student stu;
private String name;
private List<String> courses = new ArrayList<String>();
public TClass()
{
super();
}
public TClass(Student stu, String name, List<String> courses)
{
super();
this.stu = stu;
this.name = name;
this.courses = courses;
}
// 深克隆(更深一层)
public Object clone() throws CloneNotSupportedException
{
TClass tea = (TClass) super.clone();
tea.stu = (Student) tea.stu.clone();
// 指向不同引用
tea.courses = new ArrayList<String>();
// 又想保留原有的值
for (int i = 0; i < courses.size(); i++)
{
tea.courses.add(courses.get(i));
}
return tea;
}
public String toString()
{
return "TClass [stu=" + stu + ", name=" + name + ", courses=" + courses + "]";
}
......
}
Teacher [stu=Student [name=aaa, age=20], name=张老师, courses=[Java, C#]]
Teacher [stu=Student [name=bbb, age=21], name=李老师, courses=[Java, C#, oracle, spring]]
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