Java study notes - the basis of

Java foundation

Note

Write notes is a very good habit

• Single-line comments: // , shortcut keys Ctrl + /, again according to revoke comments
• Multi-line comments: / * * / , shortcut keys Ctrl + shift + / Undo Ctrl + shift + \
• Document Note: It / * * Start to *** / ** end, the shortcut keys shift + alt + j

Interestingly code comments

Identifier

In Java, class names, variable names and method names are called tags.

• Identifier should be uppercase and lowercase letters, the dollar sign $, or underscore start
• After the first character can be uppercase and lowercase letters, numbers, the dollar sign $, underscore _
• You can not use keywords as identifiers
• Identifiers are case sensitive
• Chinese and pinyin names can be used, but not recommended

Keyword

保留字
goto    const

基本类型
boolean    byte    char    double    float    int    long    short    null    true    false

类,方法和变量修饰符
abstract    class    extends    final    implements    interface    native    new
static    strictfp    synchronized    transient    volatile

访问控制
private    protected    public
    
程序控制
break    continue    return    do    while    if    else    for    instanceof    switch
case    default
    
异常处理
try    cathc    throw    throws

包相关
import    package

变量引用
super    this    void 

type of data

Basic data types

type name	Keyword	used internal memory	Ranges
Byte	byte	1 byte	-128~127
Short integer	short	2 bytes	-32768~32767
Integer	int	4 bytes	-2147483648~2147483647
Long integer	long	8 bytes	-9223372036854775808L ~ 9223372036854775807L
Single-precision floating-point	float	4 bytes	+/- 3.4E + 38F (6 ~ 7 significant digits)
Double-precision floating-point	double	8 bytes	+/- 1.8E + 308 (15 significant digits)
Character	char	2 bytes	ISO single character set
Boolean	boolean	1 byte	true or false

FIG Java data type structures

Example :

        //整数
        int a = 10;
        short b = 100;
        long c = 1000L;
        byte d = 1;
        //浮点型
        float f = 1.1F;
        double e = 3.14;
        //字符
        char ch = 'a';
        //字符串
        String str = "Hello";
        boolean flag = true;