JAVA Basics String Basic Operations

String str = "str";

str.length(); //3 Returns the length of the string

str.indexOf("s"); //0 Returns the index of s starting from 0; if not, returns -1

str.trim(); //"str" ​​Remove the spaces before and after str

str.substring(0,1); //"s" includes the beginning but not the end

str.charAt(0); // 's' Get the 0th character

str.startsWith("s") //true Whether it starts with s

str.endsWith("r") //true Whether it ends with r

str.toLowerCase() / /Convert all str to lowercase

str.toUpperCase() //Convert all str to uppercase

str.valueOf() //Convert the parameters brought in into string