赵帮辉中英文翻译(7)

Runtime (Runtime) term perspective emphasizes the dynamic process of the dynamic changes when the program is running, but also with the expression of the runtime environment similar to the meaning of the word.

Java technology is a lot of work done at run time, such as strengthening security code verification operations.

In general, Java technology runtime environment performs the following three major tasks: ? loading code - the implementation by the class loader

Class loader for the implementation of the procedures required to load all classes (as far as possible and not necessarily the same).

? validation code - the implementation of the byte code verifier

Java code before the actual operation after several tests. Byte code verifier for four times on the validation code, which can ensure code compliance and does not destroy the JVM specification system integrity. If - Check forged pointers, object access rights violation or attempt to change the object type of illegal code.

? code execution - from the implementation of the runtime interpreter ? Automatic garbage collection

Many programming languages allow programs running in the memory block dynamically allocated, the process of allocating memory blocks because of the language syntax varies, but always point to the store to return to the starting position of the pointer. In C, C + + and other languages, the programmer is responsible for deallocation of memory blocks. Sometimes this is a very difficult task. Because programmers do not always know in advance when a block of memory should be released. When not in the system can be allocated memory block, it can cause the program to a standstill, this procedure is called a memory leak.

When the allocated memory block is no longer needed, the program should be canceled or the operating environment to allocate memory block.

? garbage collection is no longer needed recovery of allocated memory block.

? in other languages in general, is the programmer's responsibility to cancel the allocation.

? Java programming language provides a system-level threads to keep track of memory allocation, to complete the garbage collection:

? no longer need to check and release the memory block ? the above work can be completed automatically

? in the JVM implementation cycle, resulting in unexpected changes ? good robustness of the code

Java program to check at compile and run-time errors. Type of examination can help detect many errors early in development. Meanwhile, many integrated development tools (IDE) to compile and run the emergence of Java programs easier and a lot of integrated development tools (eg Eclipse) are free.

1.3 Object-oriented and process-oriented differences

The production of a programming language, programming is not only a technical improvement, but also includes the expression of ideas and cognitive progress.

The C language as the representative of the early part of the language, known as process-oriented language, not only because of their expression of program design is based on the basic elements of the process, in essence, is now more understanding of the computerized system the dominant ideology or control flow or data flow, constitute elements of the system is the module - processing logic.

The generation of object-oriented languages, because the understanding of the system or the abstract to a more advanced level. Cognitive thinking at this time not only closer to the real world, and its high degree of abstraction. Thus, both easy to understand on the one hand, there are also difficult to understand the other hand, to see the realm of understanding.

1.3.1 Review process-oriented thinking

Process-oriented programming language, thought and expression, can be simply summarized as the following few:

Understanding of the system structure analysis of the process - top-down, stepwise refinement to the functional decomposition;

Each function is a data processing module, which fully describe the IPO described the internal and external features of the module;

Each module is control flow, and therefore have a typical structure of the three procedures - sequence, branch, loop;

The relationship between the module by calling the preserve, which has become a function module, which is the most important process-oriented way of code reuse under way;

Although the function call parameters and return values, but the data and functions are always separate, not only with the famous assertion - program = algorithm + data, but also makes the absolute equality of the disorder have trouble - all the functions and data relationship is no limit;

If you want to use the data flow, then the data can only be produced in an appropriate time after the call function.

The main drawback of this period are: understanding the system more difficult, the systematic development of low efficiency, code reusability is poor.