Introduction to Java in Java Study Notes

First generation language: printer-pure machine language;

Second generation language: assembly;

Third generation language: C, Pascal, Fortran process-oriented language;

C ++ facing process and objective object;

Java's pure -oriented language;

# .NET Cross -Langu Platform

Java system development history and development history and Java system:

Characteristics of Java language:

An object-oriented language;

An A platform-independent language that provides an interpretation environment for program running;

A robust language that absorbs the advantages of the C/C++ language, but removes the parts that affect the robustness of the program (such as pointers, memory Application and release, etc.).

Java program running mechanism and running process:

Java virtual machine (Java virtual machine)

Garbage collection mechanism (garbage collection)

Core mechanism of Java virtual machine:

• The Java virtual machine can be understood as a CPU that uses bytecode as machine instructions;

• There are different virtual machines for different operating platforms;

• The Java virtual machine mechanism shields the differences in the underlying operating platforms and achieves "compile once, run anywhere."

Java is an interpreted language, C/C++ is a compiled language

Core mechanism of garbage collection:

• Memory space that is no longer used should be recycled - garbage collection;

• In languages ​​such as C/C++, the programmer is responsible for recycling useless memory;

• The Java language eliminates the programmer's responsibility to reclaim unused memory space; it provides a system-level thread to track the allocation of storage space, and when the JVM is idle, check and release those Memory space that can be released.

• Garbage collection runs automatically during the running of the Java program, and programmers cannot precisely control and intervene;

Java application preliminary:

• Java source files have "java" as the extension. The basic component of a source file is a class, such as the HelloWorld class in this example.

• There can be at most one public class in a source file. There is no limit to the number of other classes. If the source file contains a public class, it must be named according to the class name. //The naming should be consistent with the naming of the public class

• The execution entry point of the Java application is the main() method. It has a fixed writing format:
  public static void main(String args[]){…}

• ##Java language is strictly case-sensitive;

• Java methods are composed of statements, each statement ends with a semicolon;

• The Java language has three comment methods:

  
  
  

Summary of the first program:

• Build the programmer’s own environment;

• Use copy;

• Master the concepts of path and classpath;

• Be familiar with common mistakes;

• Familiar with the simple rules of java programs;

• Familiar with the compilation and running of java programs;

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