Java common sense and data types

The download, installation, and environment variables of the JDK were last introduced. This time we'll talk about Java's common sense and Java data types;

Common Java Development tools

Editor:

1:ultraedit;

2:editplus, etc.;

Integrated development Environment:

JBuilder (http://www.borland.com);

Eclipse (http://eclipse.org), etc.;

Main content;

1. Identifiers;

2. Keywords;

3.Java basic data type;

4. Operators;

5. Expressions and statements;

6. Branches;

7. Circulation;

8. Methods;

9. Scope of variables

10. Simple recursion;

Identifier:

In the Java language, names of features such as variables, methods, and classes are used as sequences of characters called identifiers;

The Java identifiers have the following naming conventions:

1. Identifiers are composed of letters, underscores "_", "$" or numbers.

2. Identifiers should be preceded by letters, underscores, dollar signs;

3Java identifier case sensitive, length five limit;

4. Conventional: Java identifier selection should pay attention to "see the name of" and not with the Java language keyword duplicate;

Key words:

Some special meanings are assigned in Java, and strings used for specialized purposes are called keywords;

1. All Java keywords are lowercase english strings;

2.goto and const, although never used, are also retained as Java keywords;

Java constants:

The constant value of Java is represented by a string, distinguishing between different data types.

1. If the shaping constant: 123;

2. Real-type constants: 3.14;

3. Character constant: ' A ';

4. String constants: "HelloWorld";

5.null;

Note: Distinguish between character constants and string constants;

Java variables:

Java variable is the most basic storage unit in the program, which mainly includes variable name, variable type and scope;

Java program China each variable belongs to a specific data type and must be declared before it is used, for example:

int i = 100;

float f =12.3f;

Double d = 0.123;

String s = "Hello";

In essence, a variable is actually a small area of memory, with a variable name to the visitor block area,

Therefore, each variable must be applied before the application (Declaration), and then must be in the assignment (padding content), in order to use;

Categories of variables:

1. Press the declared location:

(1), local variables: variables defined inside a method or block of statements;

(2) member variables: Also known as local variables, external methods, variables defined internally by the class

Note: The outside of the class (outside the braces corresponding to the class) cannot have the declaration of the variable;

2. The type of data that the word belongs to is divided:

(1) Basic data type variables;

(2) Apply data type variable;

Partitioning of Java data types:

Scope of the Java base data type:

Default values for Java base data types:

Java Basic data type:

There are 4 classes of 8 basic data types defined in Java:

1. Logic type--boolean;

2. Character type--char;

3. Numerical type

(1) integer type--byte,short,int,long;

(2) floating-point type--float,double;

Logical Type Boolean:

Boolean types are generally suitable for logical operations and are generally used for process control;

Boolean data only allows true to be false, and cannot replace true and false with integers 0 or 0, which differs from C language;

Character Char:

Char-type data is used to denote "characters" in the usual sense;

Character constants are single characters enclosed in single quotation marks;

Integer type:

Java each integer type has a fixed number of table range and field length, it is not affected by the stop operating system, to ensure the portability of Java programs;

The integer constants of the Java language default to int, declaring a long constant followed by ' l ' or ' l ';

Floating-point types:

The Java floating-point constant defaults to double, and if you want to declare a constant of type float, you need to call ' F ' or ' F ' after the number;

Java common sense and data types