import java.util.List;
import java.util.Set;
public class EquTypeDao {
StringBuilder sb=new StringBuilder();
sb.append("[");//这一行出错,为什么? public String get(){
StringBuilder sb=new StringBuilder();
sb.append("[");//这一行可以用 }
public static void main(String[] args) {
StringBuilder sb=new StringBuilder();//这里也可以用
sb.append("[");
sb.append(" ");
sb.append("]");
System.out.println(sb.toString());
}
}
上面是我写的代码,主要想用一下StringBuilder,可是在EquTypeDao里不能使用,但在main,get里却可以用,不知道是什么原因,希望大家帮我解决一下。谢谢。
import java.util.Set;
public class EquTypeDao {
StringBuilder sb=new StringBuilder();
sb.append("[");//这一行出错,为什么? public String get(){
StringBuilder sb=new StringBuilder();
sb.append("[");//这一行可以用 }
public static void main(String[] args) {
StringBuilder sb=new StringBuilder();//这里也可以用
sb.append("[");
sb.append(" ");
sb.append("]");
System.out.println(sb.toString());
}
}
上面是我写的代码,主要想用一下StringBuilder,可是在EquTypeDao里不能使用,但在main,get里却可以用,不知道是什么原因,希望大家帮我解决一下。谢谢。
注意:你让一个对象去执行某个方法必须放在方法体里面!
要知道:类里面只有方法(行为)和属性(成员变量)!
StringBuilder sb=new StringBuilder(); //属性
public static void main(String[] args) //方法
public String get()//方法
public class Test {
{
StringBuilder sb=new StringBuilder();
sb.append("[");//这样没错
System.out.println(sb.toString());
}
public static void main(String[] args){
new Test();
}
}
用大括号括起来就可以了
例如:
你出错的地方改为:
String str = sb.append("[");// 这样就可以饶过编译器
也达到了你自己想要的结果
恩,确实输出了,昨天可能没注意到那么象这种,代码块的情况,在实际项目中,会怎么运用??wuhaozhiyuan?谢谢
import java.util.Set;
public class EquTypeDao {
StringBuilder sb=new StringBuilder();
sb.append("[");//这一行出错,为什么?
//类体内只能有属性和方法public String get(){
StringBuilder sb=new StringBuilder();
sb.append("[");//这一行可以用 }
public static void main(String[] args) {
StringBuilder sb=new StringBuilder();//这里也可以用
sb.append("[");
sb.append(" ");
sb.append("]");
System.out.println(sb.toString());
} }
在没有public构造器的静态类中,需要对一些属性进行初始化,
这时就会用到静态代码块
例如:hibernate的session工厂中package com.sessionFactory;import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.cfg.Configuration;/**
* Configures and provides access to Hibernate sessions, tied to the
* current thread of execution. Follows the Thread Local Session
* pattern, see {@link http://hibernate.org/42.html }.
*/
public class HibernateSessionFactory { /**
* Location of hibernate.cfg.xml file.
* Location should be on the classpath as Hibernate uses
* #resourceAsStream style lookup for its configuration file.
* The default classpath location of the hibernate config file is
* in the default package. Use #setConfigFile() to update
* the location of the configuration file for the current session.
*/
private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
private static final ThreadLocal threadLocal = new ThreadLocal();
private static Configuration configuration = new Configuration();
private static org.hibernate.SessionFactory sessionFactory;
private static String configFile = CONFIG_FILE_LOCATION; static {
try {
configuration.configure(configFile);
sessionFactory = configuration.buildSessionFactory();
} catch (Exception e) {
System.err
.println("%%%% Error Creating SessionFactory %%%%");
e.printStackTrace();
}
}
private HibernateSessionFactory() {
}
/**
* Returns the ThreadLocal Session instance. Lazy initialize
* the <code>SessionFactory</code> if needed.
*
* @return Session
* @throws HibernateException
*/
public static Session getSession() throws HibernateException {
Session session = (Session) threadLocal.get(); if (session == null || !session.isOpen()) {
if (sessionFactory == null) {
rebuildSessionFactory();
}
session = (sessionFactory != null) ? sessionFactory.openSession()
: null;
threadLocal.set(session);
} return session;
} /**
* Rebuild hibernate session factory
*
*/
public static void rebuildSessionFactory() {
try {
configuration.configure(configFile);
sessionFactory = configuration.buildSessionFactory();
} catch (Exception e) {
System.err
.println("%%%% Error Creating SessionFactory %%%%");
e.printStackTrace();
}
} /**
* Close the single hibernate session instance.
*
* @throws HibernateException
*/
public static void closeSession() throws HibernateException {
Session session = (Session) threadLocal.get();
threadLocal.set(null); if (session != null) {
session.close();
}
} /**
* return session factory
*
*/
public static org.hibernate.SessionFactory getSessionFactory() {
return sessionFactory;
} /**
* return session factory
*
* session factory will be rebuilded in the next call
*/
public static void setConfigFile(String configFile) {
HibernateSessionFactory.configFile = configFile;
sessionFactory = null;
} /**
* return hibernate configuration
*
*/
public static Configuration getConfiguration() {
return configuration;
}}