Basic Java syntax and basic java syntax

Basic Java syntax and basic java syntax

I. Cross-row

Java variables cannot be cross-row, such as: String na

Me = "James ";

The String cannot be a cross-line String, for example, String a = "xxxxxxxxxx

Yyyyyyyy ";

 

Ii. identifier rules

Java identifiers refer to the names of variables, classes, and methods. The Java language is case sensitive. An identifier can consist of letters, numbers, underscores, and dollar signs ($). A digit cannot start. The identifier cannot contain spaces.

　　

Iii. Data Type Classification

Java supports two types: basic type and reference type.

Basic Type:

• Boolean Type:
• Numeric type: Integer type (byte, short, int, long, char), floating point type (float, double)

Reference Type: Class, interface, array, null type

4. Note the following types:

Java integers are of the int type by default, for example, byte a = 56; (the system will assign 56 to a byte variable), long bigValue = 9999999999999999; (at this time, the system will not assign a value to the long variable, but assign a value to the int variable because it cannot store the variable and reports an error.) long bigValue = 999999999999999L can only be stored in this way;

The Unicode character set used by Java is used as the encoding method. A char variable in Java is a 16-bit unsigned integer, which is different from the Char in C language.

The Java floating point type is double by default. If you want to treat a floating point value as a float type, write float f = 5.12f;

The Java language also provides three special floating point values: POSITIVE_INFINITY, NEGATIVE_INFINITY, and NaN ); if a positive number is divided by 0, positive infinity is obtained. If a negative number is divided by 0, negative infinity is obtained. If a negative number is divided by 0.0, a non-number is obtained.

V. New Features of Java 7

Add a binary integer, which is expressed as 0B. If the binary number has 32 bits, the highest bits represent the symbol bits, for example, int val = 0b000000000000000000000000000000000000011. The highest bits represent the symbol bits. A value of 1 indicates a negative number, and a negative number indicates a supplemental code for storage. You must convert it to the original code to see its value. If you want to represent 64-bit binary, add l or L after the binary;

The underline function is added in Java 7, such as double pi = 3.14 _ 15_92_65_36;