String类常用方法

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字符串-分割：split

String s = "a,b,cd,efg";
String[] strs = s.split(",");

字符串-拼接：StringBuilder

StringBuilder stringBuilder = new StringBuilder().append("abc").append(1).append('d');

String new_str = stringBuilder.toString();

字符串-截取：substring

//index从标号0开始算，截取包括前，但包括后
String ss1 = str.substring(index, index + 30);

取字符串的 某个字符：charAt

char c = attr.charAt(0);//首字符

大小写转换：toUpperCase

char c1 = Character.toUpperCase(c);

查下标：indexOf

public void test02() throws Exception{
    String str = "1234567";
    int i = str.indexOf("5");//从0开始
    System.out.println("====="+i);
}