Java 浅拷贝,深拷贝
从Java 强引用。软引用,弱引用http://blog.csdn.net/jltxgcy/article/details/35558465一文中,我们看到把一个对象赋值给另一个对象,本质上是添加了引用计数。可是它们都指向相同的堆内存。它们是一个对象。假设我们想要一个独立的对象。改怎么办呢?答案是clone。
1、浅拷贝
浅拷贝是指拷贝对象时只拷贝对象本身(包括对象中的基本变量),而不拷贝对象包括的引用指向的对象。
ShallowCopy.java
class Professor0 implements Cloneable { String name; int age; Professor0(String name, int age) { this.name = name; this.age = age; } public Object clone() throws CloneNotSupportedException { return super.clone(); } } class Student0 implements Cloneable { String name;// 常量对象。 int age; Professor0 p;// 学生1和学生2的引用值都是一样的。
Student0(String name, int age, Professor0 p) { this.name = name; this.age = age; this.p = p; } public Object clone() { Student0 o = null; try { o = (Student0) super.clone(); } catch (CloneNotSupportedException e) { System.out.println(e.toString()); } return o; } } public class ShallowCopy { public static void main(String[] args) { Professor0 p = new Professor0("wangwu", 50); Student0 s1 = new Student0("zhangsan", 18, p); Student0 s2 = (Student0) s1.clone(); s2.p.name = "lisi"; s2.p.age = 30; s2.name = "z"; s2.age = 45; System.out.println("学生s1的姓名:" + s1.name + "\n学生s1教授的姓名:" + s1.p.name + "," + "\n学生s1教授的年纪" + s1.p.age);// 学生1的教授 } }
结果:
s2.p改变了s1.p的内容。而s2.name和s2.age没有改变s1.name和s1.age的内容。
2、深拷贝
深拷贝不仅拷贝对象本身。并且拷贝对象包括的引用指向的全部对象。
class Professor implements Cloneable {
String name;
int age;
Professor(String name, int age) {
this.name = name;
this.age = age;
}
public Object clone() {
Object o = null;
try {
o = super.clone();
} catch (CloneNotSupportedException e) {
System.out.println(e.toString());
}
return o;
}
}
class Student implements Cloneable {
String name;
int age;
Professor p;
Student(String name, int age, Professor p) {
this.name = name;
this.age = age;
this.p = p;
}
public Object clone() {
Student o = null;
try {
o = (Student) super.clone();
} catch (CloneNotSupportedException e) {
System.out.println(e.toString());
}
o.p = (Professor) p.clone();
return o;
}
}
public class DeepCopy {
public static void main(String args[]) {
long t1 = System.currentTimeMillis();
Professor p = new Professor("wangwu", 50);
Student s1 = new Student("zhangsan", 18, p);
Student s2 = (Student) s1.clone();
s2.p.name = "lisi";
s2.p.age = 30;
System.out.println("name=" + s1.p.name + "," + "age=" + s1.p.age);// 学生1的教授不改变。
long t2 = System.currentTimeMillis();
System.out.println(t2-t1);//耗时
}
}
结果:
s2.p不能改变s1.p的内容。
由于是不同对象。
3、当然我们另一种深拷贝方法。就是将对象串行化:
可是串行化却非常耗时,在一些框架中,我们便能够感受到,它们往往将对象进行串行化后进行传递。耗时较多。
DeepCopy2.java
import java.io.*; //Serialization is time-consuming class Professor2 implements Serializable { /** * */ private static final long serialVersionUID = 1L; String name; int age; Professor2(String name, int age) { this.name = name; this.age = age; } } class Student2 implements Serializable { /** * */ private static final long serialVersionUID = 1L; String name;// 常量对象。
int age; Professor2 p;// 学生1和学生2的引用值都是一样的。 Student2(String name, int age, Professor2 p) { this.name = name; this.age = age; this.p = p; } public Object deepClone() throws IOException, OptionalDataException, ClassNotFoundException { // 将对象写到流里 ByteArrayOutputStream bo = new ByteArrayOutputStream(); ObjectOutputStream oo = new ObjectOutputStream(bo); oo.writeObject(this); // 从流里读出来 ByteArrayInputStream bi = new ByteArrayInputStream(bo.toByteArray()); ObjectInputStream oi = new ObjectInputStream(bi); return (oi.readObject()); } } public class DeepCopy2 { /** * @param args */ public static void main(String[] args) throws OptionalDataException, IOException, ClassNotFoundException { long t1 = System.currentTimeMillis(); Professor2 p = new Professor2("wangwu", 50); Student2 s1 = new Student2("zhangsan", 18, p); Student2 s2 = (Student2) s1.deepClone(); s2.p.name = "lisi"; s2.p.age = 30; System.out.println("name=" + s1.p.name + "," + "age=" + s1.p.age); // 学生1的教授不改变。
long t2 = System.currentTimeMillis(); System.out.println(t2-t1);//耗时 } }
结果:
s2.p不能改变s1.p的内容。
由于是不同对象。
从图中也能看出将对象进行串行化后进行传递,耗时较多。