package com.zhang.String.Demo01;import java.util.Arrays;public class Demo02 {public static void main(String[] args) {String str = "java is the best language in the world, javan is awesome";//length(); returns the length of the stringSystem.out.println(str.length());//charAt(int index) returns the character at a certain positionSystem.out.println(str.charAt(str.length()-2));//Get the last one (counting from the back to the front, the first - a few)//contains (String str); determine if a string is containedSystem.out.println(str.contains("edfsd"));System.out.println(str.contains("world"));System.out.println("==============================================================");//toCharArray() returns the array corresponding to the stringSystem.out.println(Arrays.toString(str.toCharArray()));//indexOf() returns the position of the first occurrence of the stringSystem.out.println(str.indexOf("java"));System.out.println(str.indexOf("java",4));//Look back from the fifth corner mark//lastIndexOf() returns the position of the last occurrence of the stringSystem.out.println(str.lastIndexOf("java"));System.out.println("======================================================");String str2 = "Hello World";//trim() removes the spaces before and after the stringSystem.out.println(str2.trim());//toUpperCase() convert lowercase to uppercase toLowerCase convert uppercase to lowercaseSystem.out.println(str2.toUpperCase());System.out.println(str2.toLowerCase());//endWith(str) determines whether it ends with XX starWith (str) determines whether it starts with xxString str3 = "hello java";System.out.println(str3.endsWith("java"));System.out.println(str3.startsWith("hello"));System.out.println("================================================");//replace(char old, char new) replace the old character with the new characterSystem.out.println(str.replace("java","php"));//split() classifies stringsString say = "java is the best programming language,java";String[] arr = say.split("[ ,]+");//Use space sum, split + means space sum, there can be multiplefor (String string : arr){System.out.println(string);}//equalsString s1 = "hello";String s2 = "HELLO";System.out.println(s1.equalsIgnoreCase(s2));//Ignore case}}

Variable String

StringBuffer; variable-length string, slow and thread-safe.

StingBuilder; variable-length strings, fast, thread-unsafe

package com.zhang.baozhuang.Demo01;public class Demo03 {public static void main(String[] args) {StringBuffer sb = new StringBuffer();//append(); appendsb.append("java world first");System.out.println(sb.toString());sb.append("java is really fragrant");System.out.println(sb.toString());sb.append("java awesome");System.out.println(sb.toString());//insert() addsb.insert(0,"I am at the front");System.out.println(sb.toString());// replace() replacesb.replace(0,4,"hello");//Including the head but not the tail//de;ete() deletesb.delete(0,5);System.out.println(sb.toString());// clearsb.delete(0,sb.length());System.out.println(sb.toString());}}

StringBuider is used in the same way as above.