Java课件第三章

1、12345678910111213141516171819 2021 p p u u b b l l i i c c c c l l a a s s s s c c 1 1 p p u u b b l l i i c c i i n n t t x x ; ; i i n n t t y y ; ; p p r r i i v v a a t t e e i i n n t t z z ; ; p p u u b b l l i i c c v v o o i i d d m m 1 1 ( ( ) ) v v o o i i d d m m 2 2 ( ( ) ) p p r r i i v

2、 v a a t t e e v v o o i i d d m m 3 3 ( ( ) ) p p u u b b l l i i c c c c l l a a s s s s c c 2 2 c c 1 1 o o = = n n e e w w c c 1 1 ( ( ) ) ; ; c c a a n n a a c c c c e e s s s s o o . . x x ; ; c c a a n n a a c c c c e e s s s s o o . . y y ; ; c c a a n n n n o o t t a a c c c c e e s s s s o

3、 o . . z z ; ; c c a a n n i i n n v v o o k k e e o o . . m m 1 1 ( ( ) ) ; ; c c a a n n i i n n v v o o k k e e o o . . m m 2 2 ( ( ) ) ; ; c c a a n n n n o o t t i i n n v v o o k k e e o o . . m m 3 3 ( ( ) ) ; ; p p a ac ck ka ag ge e p p 1 1; ; p p a ac ck ka ag ge e p p 2 2; ; p p u u b b l

4、 l i i c c c c l l a a s s s s c c 3 3 c c 1 1 o o = = n n e e w w c c 1 1 ( ( ) ) ; ; c c a a n n a a c c c c e e s s s s o o . . x x ; ; c c a a n n n n o o t t a a c c c c e e s s s s o o . . y y ; ; c c a a n n n n o o t t a a c c c c e e s s s s o o . . z z ; ; c c a a n n i i n n v v o o k k e

5、 e o o . . m m 1 1 ( ( ) ) ; ; c c a a n n n n o o t t i i n n v v o o k k e e o o . . m m 2 2 ( ( ) ) ; ; c c a a n n n n o o t t i i n n v v o o k k e e o o . . m m 3 3 ( ( ) ) ; ; 2223 2425262728293031323334/ before constructor/ re-initialize t3/ after constructor/ at end/ shows that construction

6、 is done353637383940414243444546flower(int petals)flower(int petals)flower(string ss)flower(string ss)flower(string s, int petals)flower(string s, int petals)/! this(s); / cant call two!/! this(s); / cant call two!flower()flower()/! this(11); / not inside non-constructor!/! this(11); / not inside no

7、n-constructor!47484950515253545556575859606162636465class a void b(int x) void b(int i) class a void b(integer x) void b(int i) class a void b( ) void b(int i) class a void b(int x,int j) void b(int i) 66class a int b(int a, int j) int b(int j,int a) class a boolean t; void b(boolean t ) void b(bool

8、ean s) class a int b(int j, char a) int b(char j, int a)class a int b(int a) boolean b(int j) 6768697071727374class super public int i=0; public super(string text) i=1;public class sub extends super public sub(string text) i=2; public static void main(string ag) sub sub=new sub(“hello”); system.out.

9、println(sub.i); 75子类调用构造方法前子类调用构造方法前,缺省调用无参的缺省调用无参的, 为为保证继承链上的连续保证继承链上的连续性性,添加一个无参的添加一个无参的public b( ) 7677787980818283848586878889909192public class test public static void main(string args) m(new graduatestudent(); m(new student(); m(new person(); m(new object(); public static void m(object x) syst

10、em.out.println(x.tostring(); class graduatestudent extends student class student extends person public string tostring() return student; class person extends object public string tostring() return person; 93 dynamic binding works as follows: suppose an object o is an instance of classes c1, c2, ., c

11、n-1, and cn, where c1 is a subclass of c2, c2 is a subclass of c3, ., and cn-1 is a subclass of cn. that is, cn is the most general class, and c1 is the most specific class. in java, cn is the object class. if o invokes a method p, the jvm searches the implementation for the method p in c1, c2, ., c

12、n-1 and cn, in this order, until it is found. once an implementation is found, the search stops and the first-found implementation is invoked. cn cn-1 . . . . . c2 c1 object since o is an instance of c1, o is also an instance of c2, c3, , cn-1, and cn 94 . 9596979899/! final value v4; / pre-java 1.1 error; no