========================================================================
获取字符串长度
String st = "bacdeg";
System.out.println(st.length());
System.out.println("bacdeg".length());
执行结果：
6
6
=====================================================================
判断字符串中是否包含有某个字符
String s7 = "ageheafeRTEYEWRTEWEWYWEHEhehaheh";
System.out.println(s7.length());
System.out.println(s7.contains("a"));
System.out.println("ageheafeRTEYEWRTEWEWYWEHEhehaheh".contains("a"));
System.out.println(s7.contains("aT"));
System.out.println("ageheafeRTEYEWRTEWEWYWEHEhehaheh".contains("aT"));
执行结果：
32
true
true
false
false
=============================================================================
将字符串全部变为小写或者大写
String s7 = "ageheafeRTEYEWRTEWEWYWEHEhehaheh";
System.out.println(s7.toLowerCase()); ——全部变为小写
System.out.println(s7.toUpperCase()); ——全部变为大写
执行结果：
ageheaferteyewrtewewywehehehaheh
AGEHEAFERTEYEWRTEWEWYWEHEHEHAHEH
=============================================================================
判断字符串是否以某个（串）字符开头或者结尾
String s7 = "ageheafeRTEYEWRTEWEWYWEHEhehaheh";
System.out.println(s7.startsWith("age"));
System.out.println(s7.startsWith("ageG"));
System.out.println(s7.endsWith("heh"));
System.out.println(s7.endsWith("heha"));
执行结果：
true
false
true
false
============================================================================
判断两串字符串是否完全相等
String s7 = "ageheafeRTEYEWRTEWEWYWEHEhehaheh";
System.out.println(s7.equals("ageheaferteyewrtewewywehehehaheh"));
System.out.println(s7.equals("AGEHEAFERTEYEWRTEWEWYWEHEHEHAHEH"));
System.out.println(s7.equals("ageheafeRTEYEWRTEWEWYWEHEhehaheh"));
System.out.println(s7.equals("ageheafeRTEYEWRTEWEWYWEHEhehaheh "));
执行结果：
false
false
true
false
============================================================================
忽略大小写，判断两串字符串是否完全相等
String s7 = "ageheafeRTEYEWRTEWEWYWEHEhehaheh";
System.out.println(s7.equalsIgnoreCase("ageheaferteyewrtewewywehehehaheh"));
System.out.println(s7.equalsIgnoreCase("AGEHEAFERTEYEWRTEWEWYWEHEHEHAHEH"));
System.out.println(s7.equalsIgnoreCase("ageheafeRTEYEWRTEWEWYWEHEhehaheh"));
System.out.println(s7.equalsIgnoreCase("ageheafeRTEYEWRTEWEWYWEHEhehaheh "));
执行结果：
true
true
true
false
=========================================================================
替换字符为目标字符
str.replace(char oldChar , char newChar )
——oldChar：要替换的字符或者字符串；
——newChar：用于替换原来的字符串的内容；
String s15 = " a g eheafe54RTEYEWRTrh rhr EagW EWYWEH Ehehah eh ";
System.out.println(s15.replace("a","999"));
System.out.println(s15);
执行结果：
999 g ehe999fe54RTEYEWRTrh rhr E999gW EWYWEH Eheh999h eh
a g eheafe54RTEYEWRTrh rhr EagW EWYWEH Ehehah eh
==============================================================================
去除字符串开头和结尾的空格
String s14 = " a g eheafe54RTEYEWRTrh rhr EagW EWYWEH Ehehah eh ";
System.out.println(s14.length());
System.out.println(s14.trim());
System.out.println(s14.trim().length());
执行结果：
52
a g eheafe54RTEYEWRTrh rhr EagW EWYWEH Ehehah eh
50
=============================================================================
indexOf()方法返回的是搜索的字符或者字符串首次出现的位置
lastIdexOf()方法返回的是搜索的字符或者字符串最后一次出现的位置
PS：字符串的下标识是： -1——length（）-1
PS：如果没有检索到字符串S，则返回-1
String s8 = "ageheafe54RTEYEWRTrhrhrEagWEWYWEHEhehaheh";
String s9 = " ageheafe54RTEYEWRTrhrhrEagWEWYWEHEhehaheh";
String s10 = "ageheafe54RTEYEWRTrhrhrEagWEWYWEHEhehaheh ";
String s11 = " ageheafe54RTEYEWRTrhrhrEagWEWYWEHEhehaheh ";
String s12 = " ageheafe54RTEYEWRTrh rhrEagWEWYWEHEhehaheh ";
System.out.println(s8.length()); ——41
System.out.println(s9.length()); ——42
System.out.println(s10.length()); ——42
System.out.println(s11.length()); ——43
System.out.println(s12.length()); ——44
System.out.println(s8.indexOf("a"));——————0
System.out.println(s8.indexOf("e"));——————2
System.out.println(s9.indexOf("a"));——————1
System.out.println(s9.indexOf("e"));——————3
System.out.println(s9.indexOf(" "));——————0
System.out.println(s9.indexOf("z"));—————— -1
System.out.println(s9.lastIndexOf("a"));——————38
System.out.println(s9.lastIndexOf("h"));——————41
System.out.println(s9.lastIndexOf(" "));——————0
System.out.println(s9.lastIndexOf("z"));—————— -1
System.out.println(s9.lastIndexOf(""));——————42
==========================================================================
获取指定索引位置的字符
String s9 = " ageheafe54RTEYEWRTrhrhrEagWEWYWEHEhehaheh";
System.out.println(s9.charAt(0));
System.out.println(s9.charAt(1));
执行结果：
a
=====================================================================
获取子字符串——利用下标进行截取，注意下标是从0开始的，空格占用一个索引位置
（1）、substring(int beginIndex)——从指定的索引位置开始截取，直到字符串的结尾；
（1）、substring(int beginIndex,int endIndex)——从指定的索引位置开始截取，到指定索引结束；
String s13 = " a g eheafe54RTEYEWRTrh rhr EagW EWYWEH Ehehah eh ";
System.out.println(s13.substring(2));
System.out.println(s13.substring(2,29));
执行结果：
g eheafe54RTEYEWRTrh rhr EagW EWYWEH Ehehah eh
g eheafe54RTEYEWRTrh rhr
==========================================================================
字符串分隔
（1）、split( String sign)：根据给定的分隔符号对字符串进行分隔；
sign为分隔符号，如果想定义多个分隔符号，可以使用符号“|”，例如“,|=”，表示分隔符号分别为 ，和 = ；
（2）、split(String sign,int limit)：根据给定的分隔符对字符串进行拆分，并限定拆分次数；
sign为分隔符号，如果想定义多个分隔符号，可以使用符号“|”，例如“,|=”，表示分隔符号分别为 ，和 = ；
limit：模式匹配次数，如果设置为n，则分割为n-1次，得到的数组长度不会大于n，数组的最后一项，是最后匹配的分隔符以后的全部内容；
String s16 = "1,2,333,444,55,6664,75775,8y43u";
String[] firstArray = s16.split(",");
System.out.println(firstArray.length);
System.out.println("----------------");
System.out.println(firstArray[0]);
System.out.println(firstArray[1]);
System.out.println(firstArray[2]);
System.out.println("----------------");
for(String p : firstArray)
{
System.out.println(p);
}
执行结果：
8
----------------
1
2
333
----------------
1
2
333
444
55
6664
75775
8y43u
=================================================================
String s21 = "1,2=333,444=55,6664,75775,8y43u";
String[] firstArray8 = s21.split(",|=");
System.out.println(firstArray8.length);
System.out.println("----------------");
System.out.println(firstArray8[0]);
System.out.println(firstArray8[1]);
System.out.println(firstArray8[2]);
System.out.println("----------------");
for(String p : firstArray8)
{
System.out.println(p);
}
执行结果：
8
----------------
1
2
333
----------------
1
2
333
444
55
6664
75775
8y43u
String s20 = "1,2,333,444,55,6664,75775,8y43u";
String[] firstArray7 = s20.split(",",4);
System.out.println(firstArray7.length);
System.out.println("----------------");
System.out.println(firstArray7[0]);
System.out.println(firstArray7[1]);
System.out.println(firstArray7[2]);
System.out.println("----------------");
for(String p : firstArray7)
{
System.out.println(p);
}
执行结果：
4
----------------
1
2
333
----------------
1
2
333
444,55,6664,75775,8y43u
====================================================================