Using Objects (The Java™ Tutorials > Learning the Java Language > Classes and ... - The Diigo Meta page

• 26 Aug 09
  

  Lance Pedersen

  Wednesday August 26

  • we can add a statement within the Rectangle class that  prints the width and height:
  • within the Rectangle class
  • prints the width and height

  • Code that is outside the object's class must use an object reference or  expression, followed by the dot (.) operator, followed by a simple field name,  as in:  

    objectReference.fieldName 
  • the code in the CreateObjectDemo class is outside the code for the  Rectangle class. So to refer to the origin, width,  and height fields within the Rectangle object named  rectOne, the CreateObjectDemo class must use the names  rectOne.origin, rectOne.width, and rectOne.height,  respectively
  • Attempting to use the simple names width and height from the  code in the CreateObjectDemo class doesn't make sense — those fields  exist only within an object — and results in a compiler error.

  • Recall that the new operator returns a reference to an object. So  you could use the value returned from new to access a new object's fields:  

    int height = new Rectangle().height; 
  • essence, the statement calculates the default height of a Rectangle.
  • Note that after this statement has been executed, the program no longer has a  reference to the created Rectangle, because the program never stored  the reference anywhere. The object is unreferenced, and its resources are free  to be recycled by the Java Virtual Machine.
  • Here's the CreateObjectDemo code that invokes these two methods:  

    System.out.println("Area of rectOne: " + rectOne.getArea()); ... rectTwo.move(40, 72); 
  • The Java runtime environment deletes objects when it determines that they are no  longer being used. This process is called garbage collection
  • References that are held in a variable are usually dropped when the variable  goes out of scope. Or, you can explicitly drop an object reference by setting  the variable to the special value null.

  10 more annotations...

• 21 Mar 09
  

  Kalyani
  • objectReference.fieldName
  • The object is unreferenced, and its resources are free to be recycled by the Java Virtual Machine.
  • The expression new Rectangle(100, 50) returns an object reference that refers to a Rectangle object.
  • The Java runtime environment deletes objects when it determines that they are no longer being used. This process is called garbage collection
  • References that are held in a variable are usually dropped when the variable goes out of scope. Or, you can explicitly drop an object reference by setting the variable to the special value null. Remember that a program can have multiple references to the same object; all references to an object must be dropped before the object is eligible for garbage collection.
  • An object is eligible for garbage collection when there are no more references to that object

  4 more annotations...

• 12 Sep 08
  

  vaisha prabhu
  • Note that after this statement has been executed, the program no longer has a reference to the created Rectangle, because the program never stored the reference anywhere. The object is unreferenced, and its resources are free to be recycled by the Java Virtual Machine.
  • An object is eligible for garbage collection when there are no more references to that object. References that are held in a variable are usually dropped when the variable goes out of scope. Or, you can explicitly drop an object reference by setting the variable to the special value null. Remember that a program can have multiple references to the same object; all references to an object must be dropped before the object is eligible for garbage collection.

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