2005年9月的归档

When you create a variable that is an instance of a class, you are actually creating a reference to that class instance. The reference is defined to know how to access its class, but not to be tightly coupled with any particular instance. If you were to create two instances of a class, and then assign one to the other, both variables will be referencing the same object.

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; 
      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 ); 
      System.out.println( "\nAfter modifying two: " ); 
      System.out.println( "One = " + one.getNumber() ); 
      System.out.println( "Two = " + two.getNumber() ); 
   } 
} 

The output of the Number class is

Beginning:  
One = 1 

Two = 2  

After assigning two to one: 
One = 1 
Two = 1 

After modifying two: 
One = 3 
Two = 3 

From this output you can see that assigning the Number variable two to the Number variable one actually made two point to the same memory as one. Then, when two was modified, it affected the value of one.

Therefore, when you pass an object reference to a method, it is passed to that method by reference. If the method modifies the object, the original object is also modified. This is a powerful feature for performance because the Java Runtime Engine does not have to make a copy of the class when passing it to a method, but be aware of the potential side effects!

　　今天是中秋节，像我们这种在外面漂的人，只有自己找点事干了。
　　早上约了部门的人去爬香山。好久没爬山了，但这一次爬起来感觉不到一点难度，我们挑了一条小路，比较陡峭，但爬的比较带劲,不知不觉就到到了顶峰。
　　呵，人还是比较多，可能是天气比较好吧。
　　可惜，晚上，北京厚厚的云层挡住了月亮，十五的月亮十六圆，希望明天能看看big moon.
　　常去的google今天也换了新的logo,呵，谁让google的那位logo设计师是华人呢。

　　祝大家中秋节快乐，身体健康，工作顺利。
　　但也别忘了今天是九一八纪念日，让我们在吃月饼的同时，拿起大刀向鬼子的头上砍去。