java浅拷贝(shallow clone)与深拷贝(deep clone)
2017-08-21 21:51
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浅复制与深复制概念
浅复制
被复制对象的所有变量都含有与原来的对象相同的值,而所有的对其他对象的引用仍然指向原来的对象。换言之,浅复制仅仅复制所考虑的对象,而不复制它所引用的对象。深复制
被复制对象的所有变量都含有与原来的对象相同的值,除去那些引用其他对象的变量。那些引用其他对象的变量将指向被复制过的新对象,而不再是原有的那些被引用的对象。换言之,深复制把要复制的对象所引用的对象都复制了一遍。浅复制的实现:
public static void main(String[] args) throws CloneNotSupportedException { Teacher teacher = new Teacher(); teacher.setAge(20); teacher.setName("zhangsan"); Student2 s1 = new Student2(); s1.setAge(21); s1.setName("lisi"); s1.setTeacher(teacher); Student2 s2 = (Student2) s1.clone(); System.out.println(s2.getName()); System.out.println(s2.getAge()); teacher.setName("Teacher wang"); System.out.println(s2.getTeacher().getAge()); System.out.println(s2.getTeacher().getName()); } } class Teacher implements Cloneable { private int age; private String name; public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } } class Student2 implements Cloneable { private int age; private String name; private Teacher teacher; public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Teacher getTeacher() { return teacher; } public void setTeacher(Teacher teacher) { this.teacher = teacher; } @Override public Object clone() throws CloneNotSupportedException { return super.clone(); }
输出结果:
lisi 21 20 Teacher wang
对上述浅复制进行一定的修改让变成深复制:
对Teacher类也重写clone方法:
class Teacher implements Cloneable { ... @Override public Object clone() throws CloneNotSupportedException { return super.clone(); } ... }
修改Student2类的clone实现:
... @Override public Object clone() throws CloneNotSupportedException { Student2 student2 = (Student2) super.clone(); student2.setTeacher((Teacher)student2.getTeacher().clone()); return student2; } ...
返回的结果:
lisi 21 20 zhangsan
这种方式可以做到深复制的需求,但是如果有错综复杂的对象引用,显然这种方式是不可取的,下面我们用序列化的方式来实现深复制:
把对象写到流里的过程是序列化(Serilization)过程,而把对象从流中读出来的过程则叫做反序列化(Deserialization)过程。应当指出的是,写在流里的对象是一个拷贝,而原对象仍然存在于JVM里面。
在Student类中添加序列化的方法:
... public Object deepCopy() throws IOException, ClassNotFoundException { ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream oos = new ObjectOutputStream(bos); oos.writeObject(this); ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray()); ObjectInputStream ois = new ObjectInputStream(bis); return ois.readObject(); } ...
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