Java Basics Small Summary (1)

Day1:

1. The drive letter also belongs to the directory and folder;

2. The dir command under the DOS window displays the sub-files and subdirectories contained in the current directory;

3. In the system. Represents the current directory,.. Indicates the previous level of the directory;

4. The JVM virtual machine in Windows is mainly written in the C + + language, and the virtual machine is the software used to parse and execute Java programs;

5. Java is cross-platform and the JVM is not cross-platform;

6. JVM is the Java implementation of cross-platform transition (tool);

7. JRE (Running environment, responsible for running Java files) =JVM (virtual machine) + Core class library (auxiliary tools);

8. JDK = JRE + Dev kit;

9. Bin: The full name is binary, indicating the meaning of the binary. The bin is filled with tools or commands, or executable applications. The basic contents of the store are. exe files.

The% in Windows system indicates the variable name gets the corresponding variable value;

One. Javac.exe is the compiler that launches the JDK, compiles the Java file (source file) to build the binary file that the computer is familiar with, and needs to add the file type name at compile time;

Java.exe is run class file, run is no need to add file type name;

In Java, class is the beginning of a program, and the main method is the entry that represents the program's operation;

Day2:

The first character of a 1.Java identifier cannot be a number, a keyword cannot be used, a class name, a method name, and a variable belong to an identifier;

2. Constant type: Numeric, character, String, Boolean, null constant;

3. Basic Data type: Integer (Byte, short, int, long), decimal (double, float), char (char), Boolean (Boolean)

4. A bits is called 1bit (bit); 8 binary is called 1 byte (bytes), which is the smallest unit in the computer; 1byte = 8 bit; 1KB = 1024x768 byte; 1MB = KB; 1GB =1024MB; 1TB = GB;

5. Use DOS to run Java or Javac command, enter the file name, you can first write a first letter, and then use the TAB key to select the name;

6. In Java, the default is a double type, the integer default is the int type, the out-of-range int type is long, and the value is followed by L to show the difference; the float type that is out of range records decimals (by default, double) because the precision can be lost from a long range to a short range. So add an F after the data of type float;

7. Constant range in base type: Byte (1 bytes) <short (2 bytes) <int (4 bytes) <long (8 bytes) <float (4 bytes) <double (8 bytes), where char (2 bytes), A Boolean (1 bytes);

8. When the data types of the operators are the same, the values of the results are the same as their data types; When the data types around the operators are inconsistent, the result has a larger range of data types;

DAY3:

There are three types of loops available in 1.Java: While loop, Do-while Loop, for loop.

2.switch statement parentheses can only be byte, short, int, char type (followed by enumeration, String type)

Day4:

1. Three elements of the circular statement: initialization value, cyclic judgment, modification of the cyclic condition;

2. Break is used in loops and switch;

3. Continue only applies to the loop, and the following does not write the statement in this cycle, because it is nonsense, or error, that is, the statement body and continue side by side, and in the continue below, will be error; just skip the current loop once;

4. The break statement cannot write a side-by-side statement, so it is not executed, so it will be an error; directly end the current loop;

5. Dead loop: for (;;) {Loop Body} CTRL + C forces an end dead loop

6. Only static methods can be called in the static method;

7. Function in the stack memory run load, first into the first method is compressed stack to the bottom, stack memory run stack top method, run the stack;

Day5:

1. Function overloading: Homogeneous, same name, different parameter list (quantity, type, order);

2. The compiled class file is loaded into the method area by the hard disk when it is running in Java;

3. The memory address value "[" denotes a one-dimensional array, "I" for the int type, "D" for the double type; "@" for the special character; followed by a hexadecimal number to represent the address value;

4. Take a look at the bubble sort video

5. Sorting (ascending, descending)

DAY06:

1. Traversing a two-dimensional array

2. Defining objects, invoking face objects

Java Basics Small Summary (1)