Java basic comparable interface, collections class, Iterator interface, generics (Generic)

first, comparable interface, collections class

Common Algorithms for list:

• Sort (List); If you need to sort your custom classes, you have to implement the comparable interface to implement a method that compares two class sizes
• Shuffle (List); Random arrangement
• void reverse (List); Reverse order (linked efficiency)
• Copy (); Copy the collection, provided the size () is the same (length, and the difference in capacity)
• Fill (List, object), use an object to populate the entire List
• BinarySearch ();//Sort before using the binary search method

Example:

 PackageCollectiontext;Importjava.util.ArrayList;Importjava.util.Collections;Importjava.util.List; Public classText2 {@SuppressWarnings ("Unchecked")     Public Static voidMain (string[] args) {List List=NewArrayList (); List.add ("AAAA"); List.add ("QQQQ"); List.add ("CCCC"); List.add ("XXXX");        SYSTEM.OUT.PRINTLN (list); System.out.println ("-------------------------"); //Sequential arrangementCollections.sort (list);//Sort (List), sorting, if you need to sort your custom classes, you have to implement the comparable interface.//to implement a method that compares two class sizesSystem.out.println (list); //Random arrangementCollections.shuffle (list);//Shuffle (List); random arrangementSystem.out.println (list); //reverse arrangement (in reverse order)Collections.reverse (list);//void reverse (List); reverse order (linked more efficient)System.out.println (list); System.out.println ("-------------------------"); List List2=NewArrayList (); List2.add ("1"); List2.add ("2"); List2.add ("3"); List2.add ("4"); Collections.copy (List2, list);//copy (); Copies the collection if size () is the same (note the difference between length and capacity)System.out.println (LIST2); System.out.println ("-------------------------"); Collections.fill (List2,NewPerson ());//Fill (List, object), use an object to populate the entire ListSystem.out.println (LIST2); System.out.println ("-------------------------"); List List3=NewArrayList ();  for(inti = 0; I < 10; i++) {list3.add (i); }        intA = Collections.binarysearch (List3, 8);//BinarySearch (); It is important to note that sorting is preceded by a binary search method,//here is the order, not good-looking out, but must pay attention toSystem.out.println (a);    System.out.println (LIST3); }}classperson{@Override PublicString toString () {return"Person []"; }    }

Ii. Generics (Generic): it must be a reference type .

　　1, the type of the loaded collection is treated as an object, thus losing its actual type
2, when taken out in the collection needs transformation, low efficiency, error-prone

Benefits: Enhanced readability and stability of the program

Example:

 PackageCollectiontext;Importjava.util.ArrayList;Importjava.util.List; Public classTEXT3 { Public Static voidMain (string[] args) {List<String> list =NewArraylist<string> ();//This list contains only string types.List<person2> List2 =NewArraylist<person2> ();//This list can only contain Person2 type.List<student> List3 =NewArraylist<student>(); List.add ("QQQ"); List2.add (NewPerson2 ()); List2.add (NewStudent ());//student inherits the person, the reference to the parent class, to the object of the subclass, the problem of polymorphismList3.add (NewStudent ()); }}classperson2{//defines a Person2 class, which , in a more popular way, defines a Person2 type    }classStudentextendsperson2{}

three, comparable interface: A method (Comparato)

int CompareTo (T o)

Compares this object to the specified object for sorting.

• The object is smaller than the specified object and returns a negative integer (-1);
• The object is equal to the specified object and returns a 0 (0);
• The object is larger than the specified object and returns a positive integer (1);

Example:

 PackageCollectiontext;Importjava.util.ArrayList;Importjava.util.Collections;Importjava.util.List; Public classTEXT4 { Public Static voidMain (string[] args) {List<Animals> list =NewArraylist<animals>();  for(inti = 0; I < 5; i++) {List.add (NewAnimals ("name" + I, i+5));        } System.out.println (list);        Collections.sort (list);    SYSTEM.OUT.PRINTLN (list); }}classAnimalsImplementsComparable<animals> {    PrivateString name; Private intAge ;  PublicAnimals (String name,intAge ) {        Super();  This. Name =name;  This. Age =Age ; } @Override Public intcompareTo (Animals o) {//TODO auto-generated Method Stub        if( This. Age >o.age) {            return-1; } Else if( This. Age <o.age) {            return1; } Else{            return  This. Name.compareto (O.name); }} @Override PublicString toString () {return"Animals [name=" + name + ", age=" + Age + "]"; }    }

Java basic comparable interface, collections class, Iterator interface, generics (Generic)