Java编程思想读书笔记_第7章

final关键字类似const：

 1 import java.util.*;
 2
 3 public class FinalData {
 4     static Random rand = new Random(47);
 5     final int valueOne = 9;
 6     final int i4 = rand.nextInt(20);
 7     static final int INT_5 = rand.nextInt(20);
 8     public static void main(String[] args) {
 9         FinalData f = new FinalData();
10         //f.valueOne = 7;
11         //f.i4 = 7;
12         System.out.println(f);
13
14         FinalData f1 = new FinalData();
15         System.out.println(f1);
16     }
17     public String toString() {
18         return
19              "valueOne = " + valueOne
20              + " " + "i4 = " + i4
21              + " " + "INT_5 = " + INT_5;
22     }
23 }

注意到：i4和INT_5的差别：类的不同对象中INT_5只在地一个对象创建的时候初始化一次，而i4则在每个对象创建的时候初始化一次。

关于名字屏蔽和C++的原则是不同的

C++中子类的重载函数会屏蔽掉基类中的其他函数：

 1 #include <iostream>
 2
 3 class Homer {
 4 public:
 5     char doh(char c) {
 6         std::cout << "doh(char)" << std::endl;
 7         return ‘d‘;
 8     }
 9
10     float doh(float f) {
11         std::cout << "doh(float)" << std::endl;
12         return 1.0f;
13     }
14 };
15
16 class Milhouse {};
17
18 class Bart : Homer {
19 public:
20     void doh(Milhouse& m) {
21         std::cout << "doh(Milhouse)" << std::endl;
22     }
23 };
24
25 int main() {
26     Bart b;
27     //b.doh(1);
28     b.doh(‘x‘);
29     //b.doh(1.0f);
30     Milhouse m;
31     b.doh(m);
32     return 0;
33 }

而java不会

 1 class Homer {
 2     char doh(char c) {
 3         System.out.println("doh(char)");
 4         return ‘d‘;
 5     }
 6
 7     float doh(float f) {
 8         System.out.println("doh(float)");
 9         return 1.0f;
10     }
11 }
12
13 class Milhouse {}
14
15 class Bart extends Homer {
16     void doh(Milhouse m) {
17         System.out.println("doh(Milhouse)");
18     }
19
20     @Override char doh(char c) {
21         System.out.println("Bart:doh(char)");
22         return ‘c‘;
23     }
24 }
25
26 public class Hide {
27     public static void main(String[] args) {
28         Bart b = new Bart();
29         b.doh(1);
30         b.doh(‘x‘);
31         b.doh(1.0f);
32         b.doh(new Milhouse());
33     }
34 }

还有就是要注意初始化顺序

 1 class Insect {
 2     Insect() {
 3         System.out.println("Insect::Insect()");
 4     }
 5
 6     static int i = printInit("static Insect::i");
 7
 8     static int printInit(String s) {
 9         System.out.println(s);
10         return 5;
11     }
12
13     int j = printInit("Insect::j");
14 }
15
16 public class Beetle extends Insect {
17     Beetle() {
18         System.out.println("Beetle::Beetle()");
19     }
20
21     public static void main(String[] args) {
22         System.out.println("Beetle::main()");
23         new Beetle();
24     }
25
26     int k = printInit("Beetle::k");
27     static int l = printInit("static Beetle::l");
28 }