HashSet和TreeSet中最好只放入不可变对象

class

UN 

implements

Comparable

{

private

final

int

count;

public

UN()

{

this

.count=

0

;

}

public

UN(

int

count)

{

this

.count=count;

}

public

int

getCount()

{

return

this

.count;

}

public

String toString()

{

return

"R[count:"

+count+

"]"

;

}

public

boolean

equals(Object obj)

{

if

(

this

==obj)

{

return

true

;

}

if

(obj!=

null

&&obj.getClass()==UN.

class

)

{

UN r=(UN)obj;

if

(r.count==

this

.count)

{

return

true

;

}

}

return

false

;

}

public

int

compareTo(Object obj)

{

UN r=(UN)obj;

return

count>r.count? 

1

:count<r.count? -

1

:

0

;

}

}