What is the difference between shallow copy and deep copy in Java?
The difference between shallow copy and deep copy: Shallow copy: Create an object that references the same data, and changing the copy will also affect the original object. Deep copy: Create an object that contains a copy of the original object's data. Changing the copy will not affect the original object.
Shallow copy and deep copy in Java
Introduction
In Java , understanding the concepts of shallow copy and deep copy is crucial for object operations. This tutorial details the differences between the two and illustrates them with code examples.
Shallow copy
- Creates a new object that references the same underlying data of the original object.
- Any changes to the shallow copy will also be reflected on the original object, and vice versa.
- Follow the "reference to the same " principle.
Code example:
class Person { private String name; private Address address; } public class ShallowCopyDemo { public static void main(String[] args) { Person p1 = new Person(); p1.setName("John Doe"); Address addr = new Address(); addr.setStreet("123 Main St."); p1.setAddress(addr); // Shallow copy Person p2 = p1; // 更改 p2 的地址 p2.getAddress().setStreet("456 Elm St."); // p1 的地址也发生了变化 System.out.println(p1.getAddress().getStreet()); // 输出:456 Elm St. } }
In this example, p2
is a shallow copy of p1
, they References the same Address
object. Therefore, changes to the address of p2
will also affect p1
.
Deep copy
- Creates a new object that has an independent copy of the underlying data of the original object.
- Changing the deep copy will not affect the original object and vice versa.
- Follow the principle of "same content".
Code example:
Use the clone()
method or a third-party library (such as Apache Commons Lang) to implement deep copy.
Using the clone() method:
class Person implements Cloneable { private String name; private Address address; @Override public Person clone() { try { // 使用 super.clone() 创建新对象 return (Person) super.clone(); } catch (CloneNotSupportedException e) { e.printStackTrace(); } return null; } } public class DeepCopyDemo { public static void main(String[] args) { Person p1 = new Person(); p1.setName("John Doe"); Address addr = new Address(); addr.setStreet("123 Main St."); p1.setAddress(addr); // Deep copy Person p2 = p1.clone(); // 更改 p2 的地址 p2.getAddress().setStreet("456 Elm St."); // p1 的地址保持不变 System.out.println(p1.getAddress().getStreet()); // 输出:123 Main St. } }
In this example, the clone()
method is created for p1
A deep copy. Changing the address of p2
will not affect p1
because they refer to different Address
objects.
When to use deep copy or shallow copy?
- Shallow copy: Shallow copy can be performed when there are no side effects on modifying the copy of the object.
- Deep copy: When modifying the copy of the object may affect the original object, a deep copy must be made.
For example, be sure to use deep copies when caching objects or passing them to untrusted code.
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