java 什么是clone浅拷贝和深拷贝

淩亂°似流年 2022-04-25 04:38 190阅读 0赞

#### 什么是浅拷贝 ####

需要拷贝的源对象中的属性存在引用对象,拷贝后的对象中修改此引用对象的属性之后,源对象的引用值也跟着修改

#### clone方法 ####

clone()方法:对于基本类型是直接复制创建副本,对于引用类型,则是复制一个引用地址,不会复制引用所指对象

##### 1.浅拷贝案例: #####

创建两个实体对象,Person,Address

package com.yunsuibi.shallow.entity;
    		
    		public class Person implements Cloneable {
    		
    			private int age;
    			private String name;
    			private Address address;
    		
    			public Person(int age, String name, Address address) {
    				this.age = age;
    				this.name = name;
    				this.address = address;
    			}
    		
    			@Override
    			public Object clone() throws CloneNotSupportedException {
    				return super.clone();
    			}
    		
    			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 Address getAddress() {
    				return address;
    			}
    		
    			public void setAddress(Address address) {
    				this.address = address;
    			}
    		
    			public String display() {
    				return "Person [age=" + age + ", name=" + name + ", address=" + address + "]";
    			}
    		}

package com.yunsuibi.shallow.entity;
    		
    		public class Address {
    		
    			private String province;
    			private String street;
    		
    			public Address(String province, String street) {
    				this.province = province;
    				this.street = street;
    			}
    		
    			public String getProvince() {
    				return province;
    			}
    		
    			public void setProvince(String province) {
    				this.province = province;
    			}
    		
    			public String getStreet() {
    				return street;
    			}
    		
    			public void setStreet(String street) {
    				this.street = street;
    			}
    		
    			@Override
    			public String toString() {
    				return "Address [province=" + province + ", street=" + street + "]";
    			}
    		
    		}

1.测试

public static void main(String[] args) throws Exception {
    			Person person = new Person(15, "张三", new Address("四川", "天府二街"));
    	
    			Person clonePerson = (Person) person.clone();
    	
    			System.out.println(person);
    			System.out.println(clonePerson);
    	
    			System.out.println(person.display());
    			System.out.println(clonePerson.display());
    	
    			clonePerson.setName("王麻子");
    			clonePerson.setAge(20);
    			Address address = clonePerson.getAddress();
    			address.setStreet("天府四街");
    			System.out.println(person.display());
    			System.out.println(clonePerson.display());
    		}

打印结果:

com.yunsuibi.shallow.entity.Person@7852e922
    com.yunsuibi.shallow.entity.Person@4e25154f
    Person [age=15, name=张三, address=Address [province=四川, street=天府二街]]
    Person [age=15, name=张三, address=Address [province=四川, street=天府二街]]
    Person [age=15, name=张三, address=Address [province=四川, street=天府四街]]
    Person [age=20, name=王麻子, address=Address [province=四川, street=天府四街]]

注意:此时修改了address的复制对象后,源对象内容也跟着修改了,因此有了浅拷贝和深拷贝一说

#### 2.下面案例讲解常用深拷贝方式:通过序列化实现拷贝 ####

创建一个序列化对象

import java.io.ByteArrayInputStream;
    import java.io.ByteArrayOutputStream;
    import java.io.ObjectInputStream;
    import java.io.ObjectOutputStream;
    import java.io.Serializable;
    
    public class DeepClone implements Serializable{
    
    	
    	 /**
         * 利用序列化和反序列化进行对象的深拷贝
         * @return
         * @throws Exception
         */
        protected Object deepClone() throws Exception{
            //序列化
        	ByteArrayOutputStream bos = new ByteArrayOutputStream();
            ObjectOutputStream oos = new ObjectOutputStream(bos);
            oos.writeObject(this);
            //反序列化
            ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(bos.toByteArray()));
            return ois.readObject();
        }
    	
    }

Person对象修改为以下状态:

package com.yunsuibi.thorough2.entity;
    
    public class Person extends DeepClone {
    
    	private int age;
    	private String name;
    	private Address address;
    
    	public Person(int age, String name, Address address) {
    		this.age = age;
    		this.name = name;
    		this.address = address;
    	}
    
    	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 Address getAddress() {
    		return address;
    	}
    
    	public void setAddress(Address address) {
    		this.address = address;
    	}
    
    	public String display() {
    		return "Person [age=" + age + ", name=" + name + ", address=" + address + "]";
    	}
    }

Address对象修改为以下状态

package com.yunsuibi.thorough2.entity;
    
    public class Address extends DeepClone {
    
    	private String province;
    	private String street;
    
    	public Address(String province, String street) {
    		this.province = province;
    		this.street = street;
    	}
    
    	public String getProvince() {
    		return province;
    	}
    
    	public void setProvince(String province) {
    		this.province = province;
    	}
    
    	public String getStreet() {
    		return street;
    	}
    
    	public void setStreet(String street) {
    		this.street = street;
    	}
    
    	@Override
    	public String toString() {
    		return "Address [province=" + province + ", street=" + street + "]";
    	}
    
    }

2.测试

public static void main(String[] args) throws CloneNotSupportedException {
    		Person person = new Person(15, "张三", new Address("四川", "天府二街"));
            
            Person clonePerson = (Person) person.clone();
            
            System.out.println(person);
            System.out.println(clonePerson);
            
            System.out.println(person.display());
            System.out.println(clonePerson.display());
            
            clonePerson.setName("王麻子");
            clonePerson.setAge(20);
            Address address = clonePerson.getAddress();
            address.setStreet("天府四街");
            System.out.println(person.display());
            System.out.println(clonePerson.display());
    	}

打印结果:

com.yunsuibi.thorough.entity.Person@7852e922
    com.yunsuibi.thorough.entity.Person@4e25154f
    Person [age=15, name=张三, address=Address [province=四川, street=天府二街]]
    Person [age=15, name=张三, address=Address [province=四川, street=天府二街]]
    Person [age=15, name=张三, address=Address [province=四川, street=天府二街]]
    Person [age=20, name=王麻子, address=Address [province=四川, street=天府四街]]

此时修改了拷贝对象后,源对象没有跟着改变,深拷贝成功

**还有一种方式,源对象需要实现Cloneable接口,重写clone方法,其中包含的所有引用对象也需要实现Cloneable接口,重写clone,  
在源对象中clone中需要手动对引用对象进行clone并set源对象中,这种方式如果源对象中引用对象过多,代码就会冗余.不建议使用这种方式**

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