JVM is an imaginary machine (virtual) working with applications like on a real machine. JVM specification provides hardware and platform the compilation of Java code occurs. These specifications make the application
Java-based platform to be free from any of the compilation process
completed by JVM.
Java application program is created with a text file berekstensi. Java. This program produce a compiled bytecode file berekstensi. class or more.
Bytecode is a set of instructions similar machine code instructions. The difference is the engine code must be run on the computer system where the compilation intended, while running the java bytecode interpreter is available at all-platform computer systems and operating systems.
Garbage Collection
Pemrogaman many other languages that allow a programmer allocate memory on the run. However, after the allocation memories, there must be a way to put back the memory block
is that other programs can use it. In C, C + + language and
other, is a programmer who is absolutely responsible akan this. This where the programmer can make is to restore the block negligent memory so that the situation is known as memory leaks.
Java program to do the garbage collection means that the program does not need to delete own objects that are not used anymore. This facility reduces the the burden of managing memory by a programmer and reduce or eliminate The biggest source of error in the language that allows the allocation dynamic.
Code Security
Security Code terimplementasi through the use of Java in the Java Runtime Environment (JRE). Using the Java security model to protect the layer 3 system from untrusted Java Code.
- First, the class-loader to handle loading class to Java runtime interpreter. This process provides security with separate class - class that derives from the local disk with the classes taken from network. This limits the application because the Trojan classes derived from the local disk are loaded first.
- Second, the bytecode verifier before the bytecode is executed and bytecode guarantee to meet the basic rules of the Java language.
- Third, the security management application dealing with the security level can control whether the program has access to resources such as the file system, port network, the external and windowing system. After all it is finished running, the program code in execution.
- Language designed to make the code execution destroyer. Negationpointer is a big security step. Java does not recognize the operation pointer. Powerful in the hands of the programmer, The operation is a pointer extraordinary for the optimization program and the creation of efficient and awesome. However, this mode can be a disaster in the face evil programmer. Pointer is an exceptional tool for initialization not authorized. With negative operating pointer, the Java language can be more secure.
- Java has some safeguards against the applet. To prevent act with the program storage media, the applet does not allowed to open, read or write to the file markets. Because Java applets can open a browser window new, the window has the Java logo and text to identify window is opened. This prevents the pop-up window as deceptive request a username and password information.
Gambar dibawah ini menjelaskan aliran proses kompilasi dan eksekusi sebuah
program Java :
The first step in creating a Java-based program is write code in a text editor program. Sample text editor that can be used such as: notepad, vi, emacs and others. Program code that is made
then stored in a file berekstensi. java.
After creating and saving the program code, compiling the file that contains the code program using the Java Compiler. Results from a compilation bytecode file with the extension. class.
The file that contains the bytecode is then converted by akan Java Interpreter into machine language and in accordance with the type of platform used.
Also Read :Introduction JAVA language
What is JAVA Technology
Why Learn Java?
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