深拷貝 淺拷貝 賦值

深拷貝 淺拷貝 賦值

賦值：

class Teacher {
	String name = "王老師";
}

class Student{
	String name = “小A”;
	Teacher teacher = new Teacher();
}

Student s1 = new Student();
Student s2 = s1;
s1 == s2，指向的內存區域相同

拷貝：

class Teacher {
	String name = "王老師";
}

class Student implement Cloneable{
	String name = “小A”;
	Teacher teacher = new Teacher();
	
	public Object clone() throws CloneNotSuppotredException{
		return super.clone();
	}
}

Student s1 = new Student();
Student s2 = s1.clone();
s1 != s2, 指向不同的內存區域
根據 s1.teacher 語 s2.teacher的內存區相不相同分爲深拷貝和淺拷貝

s1.teacher == s2.teacher 淺拷貝

s1.teacher != s2.teacher 深拷貝

想深拷貝避免不了要使用對象的序列化和反序列化技術，所以：

1. 所有對象至少要實現Serializiable
2. 需要拷貝的對象還要實現Cloneable，如下：

	public Object clone() throws CloneNotSupportedException {
		ByteArrayOutputStream baos = null;
		ObjectOutputStream oos = null;
		ObjectInputStream ois = null;
		try {
			baos = new ByteArrayOutputStream();
			oos = new ObjectOutputStream();
			oos.writeObject(this);
			ois = ObjectInputStream(new ByteArrayInputStream(baos.toByteArray()));
			return ois.readObject();
		}finally{
			safeClose(baos);
			safeClose(oos);
			safeClose(ois);
		}
		retturn null;
	}

	public static void safeClose(Closeable closeable){
		try{
			if(closeable != null){
				closeable.close();
			}
		}catch(IOException e){
			e.printStackTrace();
		}

	}

補充：

1. 可能有的需要將上述clone函數單獨提取出來，將object傳入，那麼就要注意ObjectInputStream需要防止外部不可信的數據入侵，可以新建SafeObjectInputStream類如下：

	public class SafeObjectInputStream extends ObjectInputStream {
    	public SafeObjectInputStream(InputStream inputStream) throws IOException {
        	super(inputStream);
    	}

    	protected SafeObjectInputStream() throws IOException, SecurityException {
    	}

    	@Override
    	protected Class<?> resolveClass(ObjectStreamClass objectStreamClass) throws IOException, ClassNotFoundException {
      		if(objectStreamClass.getName().equals("com.example.whitename")){
            	return super.resolveClass(objectStreamClass);
        	}
        	throw new ClassNotFoundException(objectStreamClass.getName() + " not find");
    	}
	}