Java Basics-String

1, conceptually, the Java string is a sequence of dead Unicode characters, Java does not have a built-in string type, but in the standard Java class Library provides a predefined class, called String. strings are enclosed in "".

2, sub-string:

(Intercept string function) Substring method: String greeting = "Hello";

String s = greeting.substring (0,3); Output Result: Hel

The first parameter represents the first position that you do not want to copy (and does not include this number), the length of the string is: 3-0=3

Stitching strings with +

3. Immutable string:

A string class object is called an immutable string in a Java document: If you need to modify it, use the interception and stitching method

4. Check if strings are equal

Equals method: S.equals (t) equals returns True, otherwise false string constants and string variables can be compared

Equalsignorecase method (case insensitive)

Must not use = = To verify that two strings are equal

5, empty strings and Null strings:

Empty string: "" Length of 0 strings, empty string is a Java object

A string variable can also hold a special value named NULL, which means that no object is currently associated with the variable.

6. Code points and code units:

The Java string consists of a char sequence, and the char data type is a unit of code that uses UTF-16 encoding to represent Unicode code points.

The length method returns the number of code units required to represent the given string in UTF-16 encoding.

Example: String greeting = "Hello";

int n = greeting.length (); is 5

Calling S.charat (n) returns the unit of code for position n, where n is between 0~s.length ()-1

Java counts the code units and code points in a string starting from 0

7. String API:

The string class in Java contains more than 50 methods.

8. Build a string:

StringBuilder () constructs an empty string builder

int length () returns the number of code units in the builder or buffer

StringBuilder append (String str) appends a string and returns this

StringBuilder append (char c) appends a unit of code and returns this

StringBuilder appendcodepoint (int cp) appends a code point and converts it to one or two units of code and returns this

void Setcharat (int i,char c) Set the I unit of code to C

StringBuilder Insert (int offset,string str) inserts a string at offset position and returns this

StringBuilder Insert (int offset,char c) Inserts a unit of code at offset position and returns this

StringBuilder Delete (int startindex,int endIndex) deletes the code unit from StartIndex to EndIndex and returns this

String to String () returns a string that is the same as the builder or buffered content

Java Basics-String