Java Basic notes (iv)

generic type:
Generics: Accepts a reference data type by < Data amount type >, which acts at compile time using check
Whether the object that adds the collection belongs to that type, which translates the run-time problem to a compile-time exception, improving the security of the program
Avoid throwing classcastexception, and do not require type conversions

<> when do I use it?
When the reference data type of the operation is not deterministic, use <> pass in the data type you want to manipulate.
In fact <> is equivalent to accepting specific parameter ranges for reference data types

Application of generics in interfaces:
Instance:
public class Demo21 {
public static void Main (string[] args) {
Manager m = new manager ();
M.add (New Worker ("a", 23));
M.add (The New Worker ("AB", 21));
M.add (The New Worker ("AC", 22));

    System.out.println("delete-->" + m.del(1));    m.show();}static class Worker {    private String name;    private int age;    public Worker(String name, int age) {        super();        this.name = name;        this.age = age;    }    @Override    public String toString() {        return "Worker [name=" + name + ", age=" + age + "]";    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }}

}

Interface IManager {
public void Add (T data);

public T del(int index);public void show();

}

Class Manager implements IManager {
Private list List;
Manager () {
List = new ArrayList ();
}
@Override
public void Add (T data) {
List.add (data);
}
@Override
Public T del (int index) {
T data = list.get (index);
List.remove (index);
return data;
}
@Override
public void Show () {
Iterator it = List.iterator ();
while (It.hasnext ()) {
System.out.println (It.next ());
}
}
}

Method uses generics: When the method parameter data type is not deterministic, the generic type is used
Class Genericmethod {
public void Test (T t) {
System.out.println ("Method T with no return value");
}

public <T> T getT(T t) {    System.out.println("有返回值的方法getT");    return t;}

}

Wildcard characters:?

Qualifying Type:
? Extends e: Accepts subtypes of type E or E, upper limit
General storage of objects when AddAll ()
? Super E: Accepts the parent type of type E or E, lower bound
Commonly used to remove objects, comparators
public class Demo22 {
public static void Main (string[] args) {
Food f = new food ();
F.setfood ("Hamburg");
System.out.println (F.getfood ());
Food f1 = new food ();
F1.setfood (100);
Food F2 = new food ();
Buy (f);
Buy (F1);
Buy1 (F1);
Buy2 (f);
Buy2 (F2);
}
public static void Buy

Equals ().->key is the only

TreeMap: (Key-value) collection, sorting by key

Similar to the TreeSet

1) Natural order
2) Custom Comparator
A custom class implements the comparable interface
b Define a custom comparer class to implement the comparator interface

(Key-value) collection, sorted by key

Similar to the TreeSet

1) Natural order
2) Custom Comparator
A custom class implements the comparable interface
b Define a custom comparer class to implement the comparator interface

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Java Basic notes (iv)