标签:
1.局部代码块
位置:位于类的方法中
表示方法:{}
作用:控制变量的生命周期,减少内存消耗
demo:
public class LocalCode { public static void main(String [] args){ int y = 10; { int x = 20; System.out.println(x); } System.out.println(y);//运行到此时x变量已被垃圾收集 } }
2.构造代码块
位置:位于类中
表示方法:{}
作用:用于给每个对象进行初始化,减少代码量
demo:
public class ConstructCode { private String name; { System.out.println("construct code---"); eat();//构造器中都有该方法中,抽取出来放在此构造代码块中 } ConstructCode(){ System.out.println("drink----"); // System.out.println("eat---"); } ConstructCode(String name){ // System.out.println("eat----"); System.out.println(name +" drink----"); } private void eat(){ System.out.println("eat---"); } public static void main(String[]args){ ConstructCode c = new ConstructCode(); ConstructCode constructCode = new ConstructCode("xl"); } }
控制台输出:
"D:\Program Files\Java\jdk1.7.0_13\bin\java" -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:59499,suspend=y,server=n -Dfile.encoding=UTF-8 -classpath "D:\Program Files\Java\jdk1.7.0_13\jre\lib\charsets.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\deploy.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\javaws.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\jce.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\jfr.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\jfxrt.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\jsse.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\management-agent.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\plugin.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\resources.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\rt.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\access-bridge-64.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\dnsns.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\jaccess.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\localedata.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\sunec.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\sunjce_provider.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\sunmscapi.jar;D:\Program Files\Java\jdk1.7.0_13\jre\lib\ext\zipfs.jar;D:\cxlwork\STSworkspace\work-test\target\classes;D:\app\repository\org\springframework\spring-core\4.1.6.RELEASE\spring-core-4.1.6.RELEASE.jar;D:\app\repository\commons-logging\commons-logging\1.2\commons-logging-1.2.jar;D:\app\repository\org\springframework\spring-context\4.1.6.RELEASE\spring-context-4.1.6.RELEASE.jar;D:\app\repository\org\springframework\spring-context-support\4.1.6.RELEASE\spring-context-support-4.1.6.RELEASE.jar;D:\app\repository\org\springframework\spring-beans\4.1.6.RELEASE\spring-beans-4.1.6.RELEASE.jar;D:\app\repository\org\springframework\spring-expression\4.1.6.RELEASE\spring-expression-4.1.6.RELEASE.jar;D:\app\repository\org\springframework\spring-aspects\4.1.6.RELEASE\spring-aspects-4.1.6.RELEASE.jar;D:\app\repository\org\aspectj\aspectjweaver\1.8.5\aspectjweaver-1.8.5.jar;D:\app\repository\org\springframework\spring-aop\4.1.6.RELEASE\spring-aop-4.1.6.RELEASE.jar;D:\app\repository\aopalliance\aopalliance\1.0\aopalliance-1.0.jar;D:\app\repository\org\springframework\spring-jdbc\4.1.6.RELEASE\spring-jdbc-4.1.6.RELEASE.jar;D:\app\repository\org\springframework\spring-orm\4.1.6.RELEASE\spring-orm-4.1.6.RELEASE.jar;D:\app\repository\org\springframework\spring-tx\4.1.6.RELEASE\spring-tx-4.1.6.RELEASE.jar;D:\app\repository\org\springframework\spring-web\4.1.6.RELEASE\spring-web-4.1.6.RELEASE.jar;D:\app\repository\org\springframework\spring-webmvc\4.1.6.RELEASE\spring-webmvc-4.1.6.RELEASE.jar;D:\app\repository\mysql\mysql-connector-java\5.1.9\mysql-connector-java-5.1.9.jar;D:\app\repository\org\apache\logging\log4j\log4j-api\2.4.1\log4j-api-2.4.1.jar;D:\app\repository\org\apache\logging\log4j\log4j-core\2.4.1\log4j-core-2.4.1.jar;D:\Program Files (x86)\JetBrains\IntelliJ IDEA 14.0.3\lib\idea_rt.jar" com.raipeng.work.codeblock.ConstructCode Connected to the target VM, address: ‘127.0.0.1:59499‘, transport: ‘socket‘ Disconnected from the target VM, address: ‘127.0.0.1:59499‘, transport: ‘socket‘ construct code--- eat--- drink---- construct code--- eat--- xl drink---- Process finished with exit code 0
3.静态代码块
位置:类中
表示方法:static{}
作用:给类进行初始化;随着类的加载而执行,并且只执行一次
demo:
public class StaticCode { private String name; static { System.out.println("static"); } public StaticCode(){ System.out.println("construct"); } public StaticCode(String name){ System.out.println(name+" name construct"); } public static void main(String [] args){ StaticCode s = new StaticCode(); StaticCode staticCode = new StaticCode("xl"); } }
控制台输出如下:
static construct xl name construct Process finished with exit code 0
标签:
原文地址:http://www.cnblogs.com/bg2015-07-05/p/4974096.html