String base:

Declaration string:

String a;
String a,b;

Assignment:

String a="";//If the value is not assigned null
String b,c;
b="";
C="";

Construction method instantiation:

String a =new String();
String b =new String(a);

Character array instantiation:

Create a string using a character array

Construction method: public String (char[] value)

char[] charArray={ };
String a =new String(charArray,3,2);/*charArray Represents an array that is converted to a string.
3 Represents the number from which to start, and 2 represents the extraction of several elements*/

Split string:

Grammar: public String concat(Stringstr)//str is a string ready to be stitched at the end

String str="abc";
str=str.concat("de");
output str Display results: abcde

Get the string length:

Grammar: public int length()

String password ="1234567890";
int size =password.length();
output size Display results: 10

Gets the character at the specified position:

Grammar: public char charAt(int index)//Index is the index position to get

String name ="Kirito;
char ch =name.charAt(0);
output ch Display results: K

Gets the substring index position:

Grammar: public int indexOf(String str)//str is the substring to get

String str ="King of the world";
int index =str.indexOf("o");//Return to the first occurrence of o
 output index Display results: 5

Determine what is at the end of the string:

Grammar: public boolean endsWith(String suffix)//suffix is a string to compare with

String fileName ="HelloWorld.java";
Boolean bool1 =fileName.endsWith(".java");//This method can only determine if all strings at the end must contain all
Boolean bool2 =fileName.endsWith(".jpg");
output boo1 Display results: true
 output boo2 Display results: false

To determine the beginning of a string sentence:

Grammar: public boolean startsWith(String prefix)//prefix is the string to compare with

String str ="Would you like to fry fish with Kelly? Although being caught is a whole day's confinement, the fish is delicious, so it's worth it!";
Boolean bool1 =str.startsWith("To be with Collie");
Boolean bool2 =str.startsWith("To be with the piano");
output bool1 Display results: true
 output bool2 Display results: false

Get the string array:

Grammar: public char[] toCharArray()

String str ="Collie is here to report";
char[] ch=str.toCharArray();

Query whether a substring exists:

Grammar: public boolean contains(String string)//string is the substring to find

String str ="8888B888";
Boolean bool1 =str.contains("B");
Boolean bool1 =str.contains("A");
output bool1 Display results: true
 output bool1 Display results: false

Compare strings to be equal:

Grammar: public boolean equals(String abotherString)

String name =new String("keli");
String adv =new String("keli");
boolean bool =name.equals(adv);

Ignore case comparison:

Grammar: public boolean equalslgnoreCase(String anotherString)//AntherString Compared String

String str1 =new String("abc");
String str2 =new String("ABC");
boolean bool =str1.equalslgnoreCase(str2);

String operations:

Intercept string:

1. Intercept from the specified location:

Grammar: public String substring(int beginindex)//Location to start interception

String id ="123456789123456789";
String birthdate =id.substring(6);

2. Intercept the specified location:

Grammar: public String substring(int beginindex,int endindex)

String id="123456789123456789";
String birthdate =id.substring(6,14);

Replace string:

1. Replace the old string with the new one

Grammar: public String replace(CharSequence target,CharSequce replacement)
//target old character, replacement new character sequence

String str="1212";
String replaceStr =str.replace("one","one");
output replaceStr Display results:

2. Replace strings, support regular expressions

Grammar: public String replaceAll(String regex,String replacement)
//regex old string or regular expression, replacement new string

String str ="123456abc";
String replaceStr =str.replaceAll("\\d","?");//\d denotes any of the numbers 0~9
 output replaceStr Display results:??????abcd

3. Replace the first string

Grammar: public String replaceFirst(String regex,String replacement)
//regex old string or regular expression, replacement new string

String str ="Java";
String replaceStr =str.replaceFirst("a","A");
output replaceStr Display results: JAvA

String Split:

1. Split the string into arrays according to the specified symbol

Grammar: public String[] split(Stirng regex)//For splitting symbols

String str ="abc,def,ghi";
String[] strArray =str.split(",");

2. Limit the number of divisions

Limit the number of splits by a parameter

Grammar: public String[] split(String regex,int limit)
//regex is used to split characters, limit is used to split characters

String str ="192.168.0.1";
String[] firstArray=str.split("\\.");
String[] secondArray=str.split("\\.",2);

String case conversion:

Make the string uppercase:

Grammar: public String toUpperCase()

Make the string lowercase:

Sentence: public String toLowerCase()

String str ="abc DEF";
String strLOW =str.toLowerCase();
String strUP =str.toUpperCase();
output strLOW Display results: abc def
 output strUP Display results: AVC DEF

Remove blanks:

Remove whitespace from beginning to end

Grammar: public String trim()

String str ="    abc    ";
String shortStr =str.trim();
output shortStr Display results: abc

Remove all whitespace from the string

String str =" a b cd     e        f g     ";
String shortstr=str.replaceAll("\\s","");//Regular expression, empty content string
 output shortstr Display results: abcdefg

Format string:

Time format:

Grammar: String.format(String format,Object....args)

Date date =new Date();
String str =String.format("%tF",date);

StringBuffer (variable string):

The StringBuffer class is a thread-safe variable string sequence. It is a class that is a string buffer for a String, and its physical capacity increases automatically as the number of stored strings increases.

grammar:StringBuffer sbt =new StringBuffer();
     StringBuffer sbt =new StringBuffer("abc":;
     StringBuffer sbt =new StringBuffer(32);//The initial character sequence capacity is 32 characters

Append character sequence:

Grammar: public StringBuffer append(Object obj)

StringBuffer sbt=new StringBuffer();
sbt.append("City Fire");
sbt.append("Closure room Report");
sbt.append("Bomb injuries");
sbt.append("The piano finds its door");
output sbt Display results: The city's gun closure reported that the bomb wounded the harp found its door

Modify the character at the specified index:

Grammar: public void setCharAt(int index,char ch)

StringBuffer sbt =new StringBuffer("0123456");
sbt.setCharAt(3,'A');
output sbt Display results: 123 A56

String reverse order:

Grammar: public StringBuffer reverse()

StringBuffer sbt =new StringBuffer("1234567");
sbt.reverse();
output sbt Display results: 7654321

Delete substring:

Grammar: public StringBuffer delete(int start,int end)

StringBuffer sbt=new StringBuffer("Bag flower bell hug");
sbt.delete(2,4);//Delete from index 2 to 4, including index 2 but not index 4
 output sbt Display results: Bag hug

Similar to String:

sbt.length() Gets the length of the string sequence

sbt.charAt(5) Gets the character with index 5

sbt.indexOf("DEF") Gets the index position of the DEF string

sbt.substring(0,2) intercepts strings from index 0 to index 2

sbt.replace(2,5,"1234") replaces the character sequence from index 2 to index 5 with "1234"