Java.lang there is an interface below: comparable (comparable)

For custom objects, sort does not know the rules, so it cannot be compared. In this case, you must define the collation. There are two types of methods:

Java.lang there is an interface below: comparable (comparable)

You can have a custom object implement an interface that has only one method Comparableto (object o)

The rule is that the current object is compared to an O object, which returns an int value that the system sorts according to this value.

return value >0; (can define the return value as 1), as the current object >o object

If the current object =o object, the return value = 0;

Returns the value 〈0, such as the current object <o object. (The return value can be defined as-1)

Look at the Java code of Testarraylist.

We achieve ascending and descending permutations by returning values of 1 and 1 positions.

1  Packagetomtexts;2 3  4     Abstract classFatherclass5     {6         Abstract voidAbstractmethod ();7         voidPrintmethod ()8         {9System.out.println ("Fatherclass function!"); Ten         } One     } A     classChildClassextendsFatherclass -     { -         voidAbstractmethod () the         { -System.out.println ("ChildClass function!"); -         } -     } +      Public classtomtexts_07 -     { +      Public Static voidMain (String args[]) A     { atChildClass c=NewChildClass (); - C.abstractmethod (); - C.printmethod (); -  -     }    -}

Java.lang there is an interface below: comparable (comparable)