Java Base language

1,java keywords: goto and const are reserved keywords and are not implemented in Java. True false and Null are special literal values that, technically speaking, are not Java keywords.

2, identifier: Is the word we use in Java code.

⑴, identifiers cannot be keywords or true,false,null.

⑵, identifiers can contain letters, numbers 0-9, underscores (_), or dollar signs ($).

⑶, the first character of an identifier must be a letter, an underscore (_), or a dollar sign ($).

⑷, identifiers are of a different size, and no maximum length is specified.

3, data type: The Java language itself contains eight data types, and these eight data types, called basic types, are the basic construction units for creating classes.

Eight basic types of Java:

⑴ integer: ①byte (Size: 1 bytes, 8 bits)

②short (Size: 2 bytes, 16 bits)

③int (Size: 4 bytes, 32 bits)

④loog (Size: 8 bytes, 64 bits)

⑵ Float Type: ⑤float (Size: 4 bytes, 32 bits)

⑥duoble (Size: 8 bytes, 64 bits)

⑶ character type: ⑦char (Size: 2 bytes, 16 bits)

⑷ Boolean type: ⑧boolean (size: indeterminate, determined by the JVM)

Reference type: ① classes: Class

② Interface: INTCRFACC

③ Array

4, variables: variables are used to store data.

5, when performing mathematical expression operations in Java, there are the following automatic type hint rules:

⑴ all of the byte type, short and char types will be promoted to the int type;

⑵ if one of the operands is a long type, the result is a long type;

⑶ if one of the operands is a float type, the result is a float type;

⑷ if one of the operands is of type double, the result is a double type.

Beyond the range of 32 bits of int type, this literal cannot be considered an int type. In this case, we must add an L to the literal to indicate that the literal must be stored in a long type.

6, escape character: ①\b, backspace, ②\t, tab, ③\n, newline, ④\r, enter, ⑤\ "double quote, ⑥\ ', single quote, ⑦\\, backslash.

7, constant: You can declare a variable as a constant (that is, the amount that cannot be changed).

8, Operator:

⑴ pre-or post-increment and decrement: ++,--;

⑵ unary operator: +,-,~,! (forced conversion);

⑶ multiplication, except, take surplus: *,/,%;

⑷ Plus, minus, string connection: +,-,+;

⑸ move operator:<<,>>,>>>;

⑹ comparison operator:<,<=,>,>=,instanceof;

⑺ equality operator: ==,! =

⑻ bitwise operator:&,|,^;

⑼ Conditions and,or:&&,| | ；

⑽ three-mesh operator:? : ；

⑾ assignment Operator: =;

⑿ Extended assignment operator:*=,/=,%=,+=,-=,<<=,>>=,>>>=,&=,^=,|=;

9,java Note: ⑴ with two forward slash//, single-line comment;

⑵ with/* */, multi-line comment;

⑶ with/** */javadoc comments.

Java Base language