String types in Java

String types in Java
(1) A string type of data can represent all data types.

(2) string constants and generic strings in string:
string str0 = "Hello";//String constant "Hello" is pre-placed in the string constant pool of the data segment
String str1 = "Hello";//search for existing string constants directly from the constant pool
String str2 = new String ("Hello");//new a new string object in the heap
String str3 = new String ("Hello");//new a new string object in the heap
System.out.println (STR0 = = str1);//Print True
System.out.println (str2 = = STR3);//Print False
System.out.println (Str2.equals (STR3));//Print True

//string Type Object (whether it is a constant pool object or an object in the heap, its contents are immutable)
STR3 = str2;
STR2 = "World";
System.out.println (STR3);//print is still the string hello
(3) for string str2 = new String ("Hello"), two string objects (Hello and str) are generated, resulting in three objects (two string objects, one class object).

(4) methods commonly used in strings:

Strings compare Equals, Equalsignorecase, CompareTo, comparetoignorecase

System.out.println ("Hello". Equals ("Hello"));//Determines whether two strings are equal-----print true

System.out.println ("Hello". Equalsignorecase ("Hello"));//Ignore case comparison equal---print true

System.out.println ("Hello". CompareTo ("World"));//string comparison: First compares the ASCII code difference of the first different letter in turn, If all the same is longer than the string length----print-15

System.out.println ("Hello". Comparetoignorecase ("HelloWorld"));

A method in a string that is related to a character array

System.out.println (Str0.length ());//String length

System.out.println (Str0.charat (0));//What character is the first position of the string

char[] Strarray = Str0.tochararray ();//Convert a string to a character array
for (char Tmp:strarray) {
SYSTEM.OUT.PRINTLN (TMP);
}

Byte[] B = str0.getbytes ();//Convert a string to a byte array

System.out.println (Str0.indexof (' l '));//The subscript for the first occurrence of a character in a string

System.out.println (Str0.indexof (' l ', 3));//A string starting with the specified subscript to see the first occurrence of a character subscript.

System.out.println (Str0.lastindexof (' l '));//The last occurrence of a character in a string

String content-related methods

System.out.println (Str0.touppercase ());//Convert to full capitalization

System.out.println (Str0.tolowercase ());//convert to full lowercase

System.out.println (Str0.startswith ("wor"));//Determine what the string begins with

System.out.println (Str0.endswith ("Lo"));//Determine what the string ends with

System.out.println (Str0.contains ("ell"));//Determine if a string is in another string--contains

System.out.println (Str0.concat ("World"));//Add a string to the end of another string

System.out.println (Str0.replace (' l ', ' l '));//Replace a character in a string with a new character

System.out.println (Str0.replace ("L", "fuck"));//Replace a substring in a string with a new substring

System.out.println (str0.substring (1,3));//The string is intercepted by position, and the opening interval of the front closed

System.out.println (str0.substring (2));//The string is intercepted from this position.

The trim () method in the string:

System.out.println ("Hello World". Trim ());//Remove space before and after ————-print result: Hello World


The split () method in the string:

String date = "2016-03-02";
String[] result = Date.split ("-"); the parameter in//split is a regular expression. A simple? should be written as "\ \?"
for (String A:result) {
System.out.println (a);
}


Operation Result:
2016
03
02


If date = "03-02", the result of printing is:
03
02
The length of the result at this time is still 3, but one is an empty string. String a = "";(empty string) string a = null; (empty)

So judging if the string is valid: if (str!) = NULL &&! (Str.trim (). Equals ("")))----Two positions cannot be swapped, otherwise a null pointer exception will be reported.

String types in Java