Big Data first week summary

Finish the 4th day of it 18 Palm Java Foundation Course today:

Summary of key content:

path configuration, Java installation directory absolute path configuration to Java_home, dynamically remove the Java_home address,%java_home%/bin configuration to path, you can put to the front, this will be the fastest search.

Classpath configuration is Java Execution Java program Search order, generally configured as "%java_home%\lib\tools.jar;%java_home%\lib\dt.jar;." where "." Represents the current directory.

Classpath path can be specified directly when Java instruction executes

JAVA-CP Demo

Java-classpath Demo

From right to left, the first 1 is the same, other full counter, notice the overflow of the main data type , Byte is the representation that -128~127,-128 is obtained from 127-1, 127 of the binary is 01111111,-127 is 10000001, so-128 is 10000000,11111111 is -1,00000000 is 0, 0 is a positive number in the computer.

Conversion of the main data type, byte, short, int, long, float, double, upgrade is automatic conversion, there will be no precision missing, degraded conversion need to cast, but there will be a lack of precision.

The static method can only access variables in the call static

Operation

Short S = 3;

s=s+2;

s+=2 ;     

The second line of code will go wrong, because in the operation, S will be automatically promoted to int type. After operation or int type cannot be assigned to short type

The third line is OK, because the "+ =" operation automatically forces the conversion

<<: Equivalent to multiplying by 2

>>: Equivalent to a multiple of 2 divided by

Moving n is the power to multiply or divide by 2 by N times.

Basic syntax

Focus is for loop, double layer, three layers, general double is enough

Problems encountered:

How does the start batch start a path that contains spaces?

Start ""/affinity 3 "C:\Program Files (x86) \*"

Questions that need help

Not currently

Big Data first week summary