J2SE Base-1

1.java identifier: hellworld--Hello world can not space DataClass--dataclass# # _983--98.3 digits start. $bSS 5_C7--Class keyword

2, keyword class void goto const

3.JAVA constant "123" ' a ' 3.34 true,false;

4.java variable final int i = 100;  Type varName [=value][,varname=value]; Local variable/member variable basic/reference variable Testvar.java

5. Data type: base data type numeric integer byte short int long float float double character type (char) Boolean (Boolean) reference data type class interface Interface array

6 logical Boolean literal char java takes a Unicode integer byte short int long occupies a storage space table number range fixed not affected by the operating system floating-point float double

Double d = 3.1415;      float F = 4.5f; Testvar2.java

7. Conversion of basic data types from small to large (from large to small need to add coercion type conversion) Testconvert.java method ();

J2SE Base-1