Java编程思想读书笔记_第7章

final关键字类似const：

 import java.util.*;

 public class FinalData {
     static Random rand = new Random(47);
     final int valueOne = 9;
     final int i4 = rand.nextInt(20);
     static final int INT_5 = rand.nextInt(20);
     public static void main(String[] args) {
         FinalData f = new FinalData();
         //f.valueOne = 7;
         //f.i4 = 7;
         System.out.println(f);

         FinalData f1 = new FinalData();
         System.out.println(f1);
     }
     public String toString() {
         return
              "valueOne = " + valueOne
              + " " + "i4 = " + i4
              + " " + "INT_5 = " + INT_5;
     }
 }

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：

 #include <iostream>

 class Homer {
 public:
     char doh(char c) {
         std::cout << "doh(char)" << std::endl;
         return 'd';
     }

     float doh(float f) {
         std::cout << "doh(float)" << std::endl;
         return 1.0f;
     }
 };

 class Milhouse {};

 class Bart : Homer {
 public:
     void doh(Milhouse& m) {
         std::cout << "doh(Milhouse)" << std::endl;
     }
 };

 int main() {
     Bart b;
     //b.doh(1);
     b.doh('x');
     //b.doh(1.0f);
     Milhouse m;
     b.doh(m);
     return ;
 }

而java不会

 class Homer {
     char doh(char c) {
         System.out.println("doh(char)");
         return 'd';
     }

     float doh(float f) {
         System.out.println("doh(float)");
         return 1.0f;
     }
 }

 class Milhouse {}

 class Bart extends Homer {
     void doh(Milhouse m) {
         System.out.println("doh(Milhouse)");
     }

     @Override char doh(char c) {
         System.out.println("Bart:doh(char)");
         return 'c';
     }
 }

 public class Hide {
     public static void main(String[] args) {
         Bart b = new Bart();
         b.doh(1);
         b.doh('x');
         b.doh(1.0f);
         b.doh(new Milhouse());
     }
 }

还有就是要注意初始化顺序

 class Insect {
     Insect() {
         System.out.println("Insect::Insect()");
     }

     static int i = printInit("static Insect::i");

     static int printInit(String s) {
         System.out.println(s);
         return 5;
     }

     int j = printInit("Insect::j");
 }

 public class Beetle extends Insect {
     Beetle() {
         System.out.println("Beetle::Beetle()");
     }

     public static void main(String[] args) {
         System.out.println("Beetle::main()");
         new Beetle();
     }

     int k = printInit("Beetle::k");
     static int l = printInit("static Beetle::l");
 }