Class. forname and classloader

Write a simple class first

package org.test.three;public class Book {public Book(){System.out.println("Here is Book construction.");}public static String bookName="mybook";private int price;private String author;private boolean isSale;static{System.out.println("Here is Book static area. The bookName is:"+bookName);}public void printAllInfo(){System.out.println("All info is[bookName:"+bookName+",author:"+author+",price:"+price+",isSale:"+isSale+"]");}}

Test class

Package org. Test. Three;/*** in Java, both Class. forname and classloader can be used to load classes. * In addition to loading the. Class file of the class to JVM, class. forname also interprets the class and executes the static block in the class. * The classloader only loads the. Class file to the JVM and does not execute static content. The static block is executed only in newinstance. ** The initialize Parameter Function in class. forname (name, initialize, loader) can also control whether to Load Static blocks. * Calling the newinstance () method will call the constructor to create class objects. ** @ Author lushuaiyin **/public class testmain {/*** @ Param ARGs */public static void main (string [] ARGs) {// test 0 // book bk0 = New Book (); // class. forname /////////////////////////////////////// /// try {//// Test 1 /// class cc0 = Class. forname ("org. test. three. book "); // Test 2 // class CC12 = Class. forname ("org. test. three. book "); // book BK1 = (book) cc12.newinstance (); // bk1.printallinfo ();/ ///// The same as above //// @ suppresswarnings ("unchecked") /// class <book> cc13 = (class <book>) class. forname ("org. test. three. book "); // book BK2 = cc13.newinstance (); // bk2.printallinfo (); // * Second Class. forname (name, initialize, loader) // name: name of the loaded class; whether initialize is initialized, that is, whether to execute the static code block and initialize the variable value. Loader: Class Loader // class. forname ("XXX") is equivalent to class. forname ("XXX", true, xxx. class. getclassloader (); // * // Test 3 // class CC14 = Class. forname ("org. test. three. book ", true, org. test. three. book. class. getclassloader (); // Test 4 /// class cc15 = Class. forname ("org. test. three. book ", false, org. test. three. book. class. getclassloader (); // Test 5 // class CC16 = Class. forname ("org. test. three. book ", true, org. test. three. Book. class. getclassloader (); // book bk3 = (book) cc16.newinstance (); // bk3.printallinfo (); ///// Test 6 // class cc17 = Class. forname ("org. test. three. book ", false, org. test. three. book. class. getclassloader (); // book bk4 = (book) cc17.newinstance (); // bk4.printallinfo (); //} catch (classnotfoundexception e) {// E. printstacktrace (); //} // catch (instantiationexception e) {// E. printstacktrace (); //} catch (illegalacc Essexception e) {// E. printstacktrace (); /////////////// //// // Test 7 // class cc21 = classloader. getsystemclassloader (). loadclass ("org. test. three. book "); // Test 8 // class cc22 = org. test. three. book. class. getclassloader (). loadclass ("org. test. three. book "); // test 9 // class cc23 = classloader. getsystemclassloader (). loadclass ("org. test. three. book "); // book bk5 = (B Ook) cc23.newinstance (); // bk5.printallinfo (); // test 10 // class cc24 = thread. currentthread (). getcontextclassloader (). loadclass ("org. test. three. book "); // book bk6 = (book) cc24.newinstance (); // bk6.printallinfo (); // TEST 11 class cc25 = thread. class. newinstance (). getcontextclassloader (). loadclass ("org. test. three. book "); book BK7 = (book) cc25.newinstance (); bk7.printallinfo ();} catch (classnotfoundexception e) {e. printsta Cktrace ();} catch (instantiationexception e) {e. printstacktrace ();} catch (illegalaccessexception e) {e. printstacktrace () ;}}/ * test 0 print here is book static area. the bookname is: mybook Test 1 print here is book static area. the bookname is: mybook Test 2 print here is book static area. the bookname is: mybookhere is book construction. all info is [bookname: mybook, Author: NULL, price: 0, issale: false] Test 3 print here is book static are A. the bookname is: mybook Test 4 print (no output content) Test 5 print here is book static area. the bookname is: mybookhere is book construction. all info is [bookname: mybook, Author: NULL, price: 0, issale: false] Test 6 print here is book static area. the bookname is: mybookhere is book construction. all info is [bookname: mybook, Author: NULL, price: 0, issale: false] Test 7 print (no output content) Test 8 print (no output content) test 9 print here is book static area. the bookname is: mybookhere I S book construction. all info is [bookname: mybook, Author: NULL, price: 0, issale: false] test 10 print here is book static area. the bookname is: mybookhere is book construction. all info is [bookname: mybook, Author: NULL, price: 0, issale: false] Test 11 print here is book static area. the bookname is: mybookhere is book construction. all info is [bookname: mybook, Author: NULL, price: 0, issale: false] // when you connect to a database, the following code is called, which is actually the loading Driver Class, execute stati C. register the driver. // Class. forname ("com. mySQL. JDBC. driver "); static {try {drivermanager. registerdriver (New Driver ();} catch (sqlexception e) {Throw new runtimeexception ("can't register driver! ") ;}} // Class. forname ("oracle. JDBC. driver. oracledriver "); static {defaultdriver = NULL; timestamp = timestamp. valueof ("00:00:00. 0 "); try {If (defaultdriver = NULL) {defadriver driver = new oracledriver (); drivermanager. registerdriver (defaultdriver) ;}} catch (runtimeexception) {} catch (sqlexception ){}}*/