1.java中有虛函數,但是沒指針,那也許會有這樣的問題,那java是怎么實現多態的? java中可以肯定是有虛函數的,而且我們假如不申明為final形他默認就是虛函數.不用vitual申明. "In Java, you do not need to declare a method as virtual. Dynamic binding is the default behavior. If you do not want a method to be virtual, you tag it as final"--from <core java2 :volum I>. java中沒顯示的和c++中的指針,但是他有地址的概念的.而且所有我們申明的"對象"其實就是地址(或叫句柄),給他賦值就是把他指向一個內存單元.當然也可以改變他的指向.其實我們"對象"的賦值操作全是地址在變東,對象還是沒有變的.那也許有人會說那樣的話不是會產生很多沒有"對象"(句柄)的內存區域.是的是會產生,但是java的垃圾收集機制會給我們回收這樣的內存"泄漏".所以我們只關心我們操作的對象就行,其他的我們不用的對象的后事垃圾收集會給我們干. 明白了在java中的"對象"而非我們c++中理解的對象.而實際上是指針(句柄)那多態當然可以實現. 下面舉個"對象"賦值(引用)的例子說明,全是地址在變,而非真的內存單元. public class Number { PRivate int number;
public Number( int number ) { this.number = number; }
public int getNumber() { return this.number; }
public void setNumber( int number ) { this.number = number; }
public static void main( String[] args ) { Number one = new Number( 1 ); Number two = new Number( 2 ); System.out.println( "Beginning: " ); System.out.println( "One = " + one.getNumber() ); System.out.println( "Two = " + two.getNumber() );
// Assign two to one two = one;//在這里two這個句柄的值(即某個對象的地址)改成one這個句柄的值了.從而two和one指同時//向one以前指向的那個內存單元(對象).而two 以前指向的那個對象現在為沒有句柄連接的對象了.可能要被垃圾收集 System.out.println( "/nAfter assigning two to one: " ); System.out.println( "One = " + one.getNumber() ); System.out.println( "Two = " + two.getNumber() );
// Change the value of two two.setNumber( 3 );//two和one指向同一個單元,所以他對改單元的改變,one能感知. System.out.println( "/nAfter modifying two: " ); System.out.println( "One = " + one.getNumber() ); System.out.println( "Two = " + two.getNumber() ); } } 運行結果: Beginning: One = 1 Two = 2 After assigning two to one: One = 1 Two = 1 After modifying two: One = 3 Two = 3 Press any key to continue... java新手和學習c++的一點感受,如有不對之處,還望指出.
