Kowloon _java Development Road _1

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1.javathe white Paper

The Java Designer is used to explain the original design and the completion of the situation;

2.javaThe advantages

In Java 's white paper, java has:

1. Simplicity --java eliminates many of the less-used, incomprehensible, confusing features of C + + , which allows for simple programming without esoteric training.

The simple on the other hand is small:java now has a separate smaller class library java Mini-version for embedded devices.

2. Object-oriented (tbd)

3. Robustness - The most representative is the Java exception handling, the program has a problem can quickly find out where the problem is, Also ensure that the program does not exit but print information continues to run.

4. Multithreading --java the implementation of multithreading to the underlying operating system or line libraries to complete. By using multi-threading, we can perform specific behaviors separately with different threads.

3.jdkenvironment variable Configuration

System variables → new java_home variable.

Variable value fill in the JDK installation directory (I am E:\Java\jdk1.7.0)

System variables → find Path variable → edit

Enter%java_home%\bin at the end of the variable value ;

4.javathe BASIC program Structure4.1 javaNote:

Java is case-sensitive,

The class name must start with a letter and the first letter be capitalized

Multiple words make up the first letter of each word capitalized

4.2Data Type

The Java language is a strongly typed language, and a type must be declared for each variable, so the variable must be defined before it can be used;

There are 8 Basic Types in Java: (4 shaping,2 floating point)

Integer: Represents a number that has no fractional part, is allowed to be negative, and the long integer type is followed by L;

Byte Short int Long

Floating point: A numeric value that represents a fractional part.

float: suffix f 3.41F without F default to double type (rarely used)

Double: The value after the suffix D can be added by default;( common )

Char type: constant used to represent a character;

Boolean type: There are 2 values:false and true to determine the logical condition of the

4.3variables

Variable names are differentiated to lowercase,

After you declare a variable, you must assign a variable to use it.

Assigning a variable with a declared value requires that the variable name be placed to the left of (=) .

in Java development, the declaration of variables is as close to the first use as possible, which is a good writing style.

4.4Constants

In Java, the keyword final indicates a constant, indicating that the variable can only be assigned once. The habit is to have a constant named all uppercase.

In Java , you want constants to be used in more than one method of a class, which is typically a class constant.

4.5operator

+-*/ corresponds to subtraction 15%2 =1 to take the remainder or to take the mold

4.6Relational Operators

= = Indicates whether the values are equal

! = does not equal

&&: double and the expression and Judge both sides of the same true is true ( with short-circuit effect, when the first expression is not immediately after the condition does not execute ) .

| |: double or either one of the two is True ( with a short-circuit effect, when the first expression is not immediately followed by the condition is not performed ).

4.7Bitwise Operators

&: Single and judgment both sides are true ( regardless of whether the first expression is true or false, the program executes the second conditional expression )

| : One or both of the two are true ( Whether the first expression is true or false, The program will execute the second conditional expression. )

4.8detects whether strings are equal andStringof theAPI

String str = "Hello";

Str.equals ("Hello");// Case Sensitive

Str.equalsignorecase ("Hello");/ /Case insensitive

Str.tolowercase ();// converts a string into lowercase

Str.touppercase ();// converts a string into uppercase

Str.trim ();// Delete the string header and trailing spaces

4.9Building a String

Execution Speed: StringBuilder > StringBuffer > String

String is a character constant, and each time a connection is constructed a new string object is wasted space;

StringBuilder: Character variable thread unsafe for single-threaded operation

StringBuffer: Character variable thread safe for multithreaded operations

5.0Blocks (Block) Scope

A variable with the same name cannot be declared in a nested two block.

5.1Array

Array declaration: int [] A;

Creates a numeric array, so the element defaults to 0, the object array defaults to null, andtheboolean defaults to false .

Kowloon _java Development Road _1