关于Java的clone()

相关要点:

1.必须实现Cloneable接口，这个接口只是一个标识；如果不实现，调用了clone()，运行时会报CloneNotSupportedException

2.clone是Object的方法，标识为protected，子类必须重写，标识符可改为public

3.对于jdk1.5,clone可以返回相应类的类型或Object；对于1.4，只能返回Object

4.注意深复制和浅复制

浅复制

(1)对于int,double,Double,String等基本类型，super.clone()是采用的深复制

public class TestShallow implements Cloneable {
    public int a;
    public String b;
    public Double c;
    public TestShallow clone() throws CloneNotSupportedException{
        return (TestShallow)super.clone();
    }
}
class Test {
    public static void main(String[] args) throws CloneNotSupportedException {
        TestShallow a = new TestShallow();
        a.a = 12;
        a.b = "hahaa";
        a.c = 14.11;
        System.out.println("a原值");
        print(a);
        TestShallow b = a.clone();
        b.a = 13;
        b.b = "hahab";
        b.c = 15.11;
        System.out.println("a现值");
        print(a);
        System.out.println("b现值");
        print(b);
    }

    public static void print(TestShallow a) {
        System.out.println("a=" + a.a);
        System.out.println("b=" + a.b);
        System.out.println("c=" + a.c);
    }
}

 

 

结果:

a原值
a=12
b=hahaa
c=14.11
a现值
a=12
b=hahaa
c=14.11
b现值
a=13
b=hahab
c=15.11

(2)对其他类及自定义类，默认采用的是浅复制

class A {
    public String a;
}
public class TestShallow1 implements Cloneable {
    public int a;
    public A b;
    public TestShallow1() {
        b = new A();
    }
    public TestShallow1 clone() throws CloneNotSupportedException{
        return (TestShallow1)super.clone();
    }
}
class Test1 {
    public static void main(String[] args) throws CloneNotSupportedException {
        TestShallow1 a = new TestShallow1();
        a.a = 12;
        a.b.a = "hahaa";
        System.out.println("a原值");
        print(a);
        TestShallow1 b = a.clone();
        b.a = 13;
        b.b.a = "hahab";
        System.out.println("a现值");
        print(a);
        System.out.println("b现值");
        print(b);
    }

    public static void print(TestShallow1 a) {
        System.out.println("a=" + a.a);
        System.out.println("b=" + a.b.a);
    }
}

 

结果：

a原值
a=12
b=hahaa
a现值
a=12
b=hahab
b现值
a=13
b=hahab

深复制

对于其中非基本类型的字段，必须明确进行其赋值

class A implements Cloneable {
    public String a;
    public A clone() throws CloneNotSupportedException{
        return (A)super.clone();
    }
}
public class TestDeep implements Cloneable {
    public int a;
    public A b;
    public TestDeep() {
        b = new A();
    }
    public TestDeep clone() throws CloneNotSupportedException{
        TestDeep clone = (TestDeep)super.clone();
        clone.b = this.b.clone();
        return clone;
    }
}
class Test1 {
    public static void main(String[] args) throws CloneNotSupportedException {
        TestDeep a = new TestDeep();
        a.a = 12;
        a.b.a = "hahaa";
        System.out.println("a原值");
        print(a);
        TestDeep b = a.clone();
        b.a = 13;
        b.b.a = "hahab";
        System.out.println("a现值");
        print(a);
        System.out.println("b现值");
        print(b);
    }

    public static void print(TestDeep a) {
        System.out.println("a=" + a.a);
        System.out.println("b=" + a.b.a);
    }
}

 

结果:

a原值
a=12
b=hahaa
a现值
a=12
b=hahaa
b现值
a=13
b=hahab