JS字符串截取指定字符前后内容的实现方法

let str = 'hello, how are you doing? username!'
// 截取 ? 前面的字符串：
let before1 = str.substring(0,str.lastIndexOf("?")) // 不包含 ?
console.log(before1,'before1---------------'); // hello, how are you doing 

let before2 = str.substring(0,str.lastIndexOf("?") + 1) // 包含 ?
console.log(before2,'before2---------------'); // hello, how are you doing?

// 截取 ? 后面的字符串：
let after1 = str.substring(str.lastIndexOf("?") + 1) // 不包含 ?
console.log(after1,'after1-----------------'); // username!

let after2 = str.substring(str.lastIndexOf("?")) // 包含 ?
console.log(after2,'after2-----------------'); // ? username!

let str = 'hello? how are you doing? username!'
// 截取第一个 ? 前面的字符串
let index1 = str.indexOf("?")
let string1 = str.substring(0, index1); // 不包含 ?
console.log(string1,'string1------') // hello

let string11 = str.substring(0, index1 + 1); // 包含 ?
console.log(string11,'string11------') // hello?

// 截取第一个 ? 后面的字符串
let index2 = str.indexOf("?")
let string2 = str.substring(index2 + 1, str.length); // 不包含 ?
console.log(string2,'string2------') //  how are you doing? username!

let string22 = str.substring(index2, str.length); // 包含 ?
console.log(string22,'string22------') // ? how are you doing? username!

//截取最后一个 ? 前面的字符串
let index3 = str.lastIndexOf("?")
let string3 = str.substring(0, index3); // 不包含 ?
console.log(string3,'string3---------') // hello? how are you doing 

let string33 = str.substring(0, index3 + 1); // 包含 ?
console.log(string33,'string33---------') // hello? how are you doing?

//截取最后一个 ? 后面的字符串
let index4 = str.lastIndexOf("?")
let string4 = str.substring(index4 + 1, str.length); // 不包含 ?
console.log(string4,'string4----------') //  username!

let string44 = str.substring(index4, str.length); // 包含 ?
console.log(string44,'string44----------') //  ? username!

String a = "abcd_efgh_ijklmn_";
int index = a.indexOf("_");//获取第一个"_"的位置
String after1 = a.substring(index + 1);
System.out.println("第一个_后面字符串为：" + after1);

String a = "abcd_efgh_ijklmn_";
int index = a.indexOf("_");//获取第一个"_"的位置
String before1 = a.substring(0,index);
System.out.println("第一个_前面字符串为：" + before1);

String a = "abcd_efgh_ijklmn_";
String after2 = a.substring(a.indexOf("_",a.indexOf("_") + 1) + 1);
System.out.println("第二个_后面字符串为：" + after2);

String a = "abcd_efgh_ijklmn_";
String before2 = a.substring(0,a.indexOf("_",a.indexOf("_") + 1));
System.out.println("第二个_前面字符串为：" + before2);

String a = "abcd_efgh_ijklmn_";
String[] x = a.split("_");
System.out.print("分割后的字符为：");
for(int i = 0;i<x.length;i++){
      System.out.print(" " + x[i]);
 }

String b = "110.120.130.140.150";
String[] o = b.split("\\.");
System.out.print("分割后字符为：");
for(int i = 0;i<o.length;i++){
     System.out.print(" " + o[i]);
}