Java basics-set (3)-generic, enhanced for, tool class, java tool class

Java basics-set (3)-generic, enhanced for, tool class, java tool class

Next, Java basics-set (2)-iterator and Map set

6. Generic(1) Definition:

Generic is a special type that puts explicit types of work in the process of creating objects or calling methods.

(2) format:

<Data type>

         ArrayList<String> aList=new ArrayList<String>();

<String> indicates the generic type.

(3) Benefits: (master)

A: solved the yellow warning line problem.

B: Advance the conversion exception during the runtime to the compilation period.

C: optimized the program design, without the need for forced type conversion

 

(4) Development of generics

A: Generic

B: Generic Method

C: generic interface

 

(5) Generic usage:

Check whether there are any classes or interfaces in the API. If yes, they are generic applications.

It is generally used in a set.

7. Enhance the for Loop (new features after JDK 5)(1) format:

For (element type variable of an array or Collection set: object of an array or Collection set)

{

Use variables directly.

}

For example, in one of the map set traversal modes, the enhanced

Public static void main (String [] args) {Map <String, Integer> map = new HashMap <String, Integer> (); map. put ("Two Yang", 23); map. put ("two rows", 24); map. put ("diguang", 25); Set <String> keys = map. keySet (); // store the key to the set. for (String key: keys) {// retrieve each key by traversing the key set. <U> <span style = "color: # ff0000;"> enhanced for </span> </u> Integer value = map. get (key); // Let the key find the value get (Object key) System. out. println (key + "***" + value );}}

(2) benefits:

This facilitates the traversal of arrays and Collection sets.

(3) Note:

A: Enhancement for is used to replace the iterator.

B: Do not use the for enhancement function to traverse the set and modify the set itself.

(4) traverse the set in three ways

Iterator

Common for + get

Enhanced for (used at work)

8. Tools

There are two commonly used tool classes: Collections and Arrays.

Summary

There are many contents in the set, but they are not messy. As long as the Organization is clear, it must be clear to the chest.