關于Java的clone()

燮羽 2010-11-06

展開全文

相關要點:

1.必須實現(xiàn)Cloneable接口，這個接口只是一個標識；如果不實現(xiàn)，調(diào)用了clone()，運行時會報CloneNotSupportedException

2.clone是Object的方法，標識為protected，子類必須重寫，標識符可改為public

3.對于jdk1.5,clone可以返回相應類的類型或Object；對于1.4，只能返回Object

4.注意深復制和淺復制

淺復制

(1)對于int,double,Double,String等基本類型，super.clone()是采用的深復制

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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現(xiàn)值");

        print(a);

        System.out.println("b現(xiàn)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);

    }

}

結果:

a原值
a=12
b=hahaa
c=14.11
a現(xiàn)值
a=12
b=hahaa
c=14.11
b現(xiàn)值
a=13
b=hahab
c=15.11

(2)對其他類及自定義類，默認采用的是淺復制

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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現(xiàn)值");

        print(a);

        System.out.println("b現(xiàn)值");

        print(b);

    }



    public static void print(TestShallow1 a) {

        System.out.println("a=" + a.a);

        System.out.println("b=" + a.b.a);

    }

}

結果：

a原值
a=12
b=hahaa
a現(xiàn)值
a=12
b=hahab
b現(xiàn)值
a=13
b=hahab

深復制

對于其中非基本類型的字段，必須明確進行其賦值

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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現(xiàn)值");

        print(a);

        System.out.println("b現(xiàn)值");

        print(b);

    }



    public static void print(TestDeep a) {

        System.out.println("a=" + a.a);

        System.out.println("b=" + a.b.a);

    }

}

結果:

a原值
a=12
b=hahaa
a現(xiàn)值
a=12
b=hahaa
b現(xiàn)值
a=13
b=hahab