String类型区分大小写
String a = "Abc";
System.out.println(a.compareTo("abc")); -32 不匹配
System.out.println(a.compareTo("Abc")); 0 匹配
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String a = "ABC";
System.out.println(a.indexOf("Ab")); -1 不匹配
System.out.println(a.indexOf("AB")); 0 匹配
因此: indexOf方法是区分大小写的