CS100J, Fall 2001
Thurs 10/25
Lecture 16
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Announcements:
+ E5: 1-2 page algorithm for P5, due Tues
+ P5: actual due date (not 11/13)....
+ future reading: 6.4 for next Thurs; next, inheritance: 7.1-7.3
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Topics:
+ initializer lists
+ anonymous arrays
+ objects with arrays
+ arrays of objects (leads into multidimensional arrays, but not this time)
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Summary from Lecture 15
+ Arrays: collections of data of type; another kind of object in Java
+ array syntax:
  type[] var = new type[size]
  indexing: var[index]
  assigning: var[index] = value
  default values: elements are "zeros"
  instance variable: var.length
+ $for$
  for(init;check;incr) statements
  use for determinite loops
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Initializer lists:
+ handy way to creating an array and storing small amount of values:
  type[] var = {val,val,...}; <- the $;$ is mandatory here!
               ^^^^^^^^^^^^^^
               INITIALIZER LIST
+ MUST declare on the same line!
+ essentially a shortcut
  ex) write an init list that does the following statements:
      int[] x = new int[2]; x[0]=10; x[1]=20;


+ cannot change the size!      
+ initializer list not useful as a trick to "pass arrays":
  $return {1, 2, 3}$   won't work
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Anonymous array:
+ formal way to write as an anonymous array:
  typ[] var = new type[] {list of values};
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
                    ANONYMOUS ARRAY
+ may use anonymous arrays to pass a ref to an array WITH values
  ex) $return new int[] {1,2,3}$
      will actually return a ref to an array from a method
      $return {1,2,3}$
      will cause compiler error










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public class anonarray0 {
    public static void main(String[] args) {
	double[] r = randomArray();
	for (int i = 0; i< r.length; i++)
	    System.out.print(r[i] + " ");
	System.out.println();
    }
    // Generate an array of three values:
    
    private static ____________ randomArray() {

	return _______________ {
	    Math.random(),Math.random(),Math.random()
	};  
    }
}
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Objects with arrays:
+ one way of "faking" a collection of different types
+ some classes may have fields as arrays
+ how?
  - create arrays directly in field
  - create arrays in a constructor and/or method
+ remember: array size must not change once the array is created

see classWithArrays.java
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Arrays with objects:
+ think of the syntax type[] 
  - this syntax implies all kinds of types!
  - can be primitive types, can be classes?
+ examples: Worker[], Tray[], Blah[], etc
+ array of objects means ARRAY OF REFERENCES
  - elements hold references, not objects!
  - need to create objects for each element of array
  - default values are null
+ to access members of objects "in" an array (the refs are in the array),
  - use name[index].member
  - the $[]$ "operate" before the $.$

see personArray.java, arrayOfObjects.java
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