Static attribute / Class member variable / Class variablesĪttribute / Member variables / Instance variables Java Built in type, There is no “ Unsigned ” Of.
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Java Variables in cannot exist out of class. (3) differ C In language boolean type ,Java The only true and false is true and false and 0,1 irrelevant C Medium is 0 For false, Not 0 It's all true. (2) differ C In language char type ,Java Medium char More broadly, Not necessarily a letter, It can also be a Chinese character. (1) stay Java in, The length of each data type is fixed, It's different from C In language, It will vary according to the operating system. 2 data type data typeĬlass reference ( The string is contained in ) in other words class Not directly corresponding to the operating system of the machine, It interacts with the operating system indirectly through the virtual machine, The virtual machine interprets the program to the local system for execution. class Class files, This kind of file can be executed on a virtual machine. As a whole Java The core part of cross-platform implementation, be-all Java The program will first be compiled as. On the actual operating system 、 Just in time compilation 、 A system that runs bytecode programs, Like a virtual machine. JVM:Java virtual machine, Is to run Java Bytecode program (.class file ) Of “ operating system ”, He actually loads. Through it, too ,Java The developers can release their own programs to users, Let users use.
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JRE:Java Operating environment, Include JVM also Java SE API, If you want to run Java Program, You need to download and install. If you want to develop Java Program, You need to download it in the operating system JDK. ) and Java Basic class library ( namely Java API Include rt.jar), Can be Java The source program is compiled into Java Target program ( Bytecode ). JDK:Java Development kit for, It includes Java Running environment JRE(Java Runtime Envirnment)、 a pile Java Tools (javac/java/jdb etc. JDK = JRE(Java Runtime Envirnment) + Tools JavaSE It mainly includes JVM、Java SE API、JRE、JDK Other parts.
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) A platform for development and operation. Is the smallest of the three platforms, It's a small digital device ( Including mobile phone 、PDA etc. (3)JavaME(Java Micro Edition Miniature version ):
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Is in JavaSE A series of services are added on the basis of, Suitable for writing Web application (2)JavaEE(Java Enterprise Edition Enterprise Edition ): It is the basis of various application platforms, Writing desktop applications is very convenient (1)JavaSE(Java Standard Edition The standard version ): Stay Java In the process of development, because Java Language is used more and more widely, Different application versions are distinguished according to different levels of application development : 3.4 Single precision floating point variables.3.3 Double precision floating point variables.