（JAVA）String类之比较方法(2)

String类：
获取字符串的内容
一、获取字符串长度public int length() {return value.length;}length  与 lenght()的区别：前面是属性，不需要传参数后面是方法
二、指定下角标，返回固定位置的对应字符串public char charAt(int index) {if ((index < 0) || (index >= value.length)) {throw new StringIndexOutOfBoundsException(index);}return value[index];}
三、返回一个字符在字符串中第一次出现的位置
public int indexOf(String str) {return indexOf(str, 0);}
四、返回一个字符在指定位置后，出现的位置public int indexOf(String str, int fromIndex) {return indexOf(value, 0, value.length,str.value, 0, str.value.length, fromIndex);}
五、返回一个字符（字符串）在另一个字符串中最后一次出现的位置public int lastIndexOf(String str) {return lastIndexOf(str, value.length);}
六、获取字符串的一部分
String substring(int beginIndex,int endIndex);public String substring(int beginIndex, int endIndex) {if (beginIndex < 0) {throw new StringIndexOutOfBoundsException(beginIndex);}if (endIndex > value.length) {throw new StringIndexOutOfBoundsException(endIndex);}int subLen = endIndex - beginIndex;if (subLen < 0) {throw new StringIndexOutOfBoundsException(subLen);}return ((beginIndex == 0) && (endIndex == value.length)) ? this: new String(value, beginIndex, subLen);}
七、转换
1.将字符串转换为字节数组public byte[] getBytes(Charset charset) {if (charset == null) throw new NullPointerException();return StringCoding.encode(charset, value, 0, value.length);}
2.将字符串全部转成小写public String toLowerCase(Locale locale) {if (locale == null) {throw new NullPointerException();}int firstUpper;final int len = value.length;Now check if there are any characters that need to be changed.scan: {for (firstUpper = 0 ; firstUpper < len; ) {char c = value[firstUpper];if ((c >= Character.MIN_HIGH_SURROGATE)&& (c <= Character.MAX_HIGH_SURROGATE)) {int supplChar = codePointAt(firstUpper);if (supplChar != Character.toLowerCase(supplChar)) {break scan;}firstUpper += Character.charCount(supplChar);} else {if (c != Character.toLowerCase(c)) {break scan;}firstUpper++;}}return this;}3.将字符串全部转为大写String.toUpperCase(Locale.ROOT);4.切割，将字符串切割为指定要求的字符串数组,参数为正则表达式String[] split5,替换String replase(char oldchar.char newchar);String replase(String oldString.String newString);6.去掉字符串中两端空格去掉：String trim()7.两个字符串的字典形式比较int compareTo(String s)

import java.nio.charset.StandardCharsets;
import java.util.Locale;public class getStringDome {public static void main(String[] args){methon_1();methon_2();methon_3();menth_4();methon_5();}public static void methon_1(){String a = "asdfhgvscasdf";System.out.println(a.length());System.out.println(a.charAt(3));System.out.println(a.indexOf("s"));System.out.println(a.indexOf("s",2));System.out.println(a.lastIndexOf("s"));System.out.println(a.lastIndexOf("s",4));System.out.println(a.substring(2,5));//遍历字符串
//        for (int x = 0;x<a.length();x++){
//            System.out.println(a.charAt(x));
//        }}public static void methon_2(){byte[]  bytes="张三".getBytes(StandardCharsets.UTF_8);for (int x = 0;x < bytes.length;x++){System.out.println(bytes[x]);}byte[] c = {-27,-68,-96};String m = new String(c);System.out.println(m);}public static void methon_3(){String s1 = "AJDSKVvdknvv";s1 = s1.toLowerCase(Locale.ROOT);System.out.println(s1);String s2;s2 = s1.toUpperCase(Locale.ROOT);System.out.println(s2);}public static void menth_4(){String a ="asdkvjbwiejfhljzcnvndj";String[] a1 = a.split("j");for (int x = 0;x <a1.length;x++){System.out.println(a1[x]);}System.out.println("==========================");String b = "192.168.0.1";String[] b1 =b.split("\\.");for (int x = 0;x <a1.length;x++){System.out.println(b1[x]);}System.out.println("==========================");}public static void methon_5(){String c = "zxcvb" ;String c1 = "asdf";int c2 = c.compareTo(c1);System.out.println(c2);}

总结

1. Scanner 了解接收键盘输入
以后使用IO接收 Scanner(System.in)

2. 字符串 -- 熟练
2.1 定义方式，两种
|-- 直接定义 String s = ""
|-- new方法 String s = new String("")，不推荐使用
|-- 定义方法区别，前者一个对象，后者两个对象

2.2 字符串的底层结构--特性
|-- private final char[] value 字符串就是一个字符数组
|-- String字符串，是一个常量，不可以改变
|-- 字符串面试题。引用类型中，数组，类类型，接口，都会改变，唯一就String不变

2.3 构造器
|-- 字节数组变成字符串， new 传递字节数组，查询编码表 byte[] = {};
|-- 字符数组变成字符串， new 传递字符数组，不查询编码表 char[] = {}