String类中常用的方法

@Test
    public void demo(){

        // 以下为String中的常用的方法及注释， 最常用的注释前有**标注
        String s = "abcdefg123456";

        // 返回下标对应的ASCII码
        int codePointAt = s.codePointAt(7);
        // **返回字符串s和字符串Q的，第一个不相等字符的ASCII码差值，如果查找结束发现都相等，则返回两个字符串的长度差值
        int compareTo = s.compareTo("Q");
        // 返回下标前一位对应的ASCII码
        int codePointBefore = s.codePointBefore(7);
        // 返回代码点长度
        int codePointCount = s.codePointCount(4, 7);
        // 返回从index=4处偏移到codePointOffSet=7之后的索引
        int offsetByCodePoints = s.offsetByCodePoints(4, 7);
        // 将字符串变成字节数组
        byte[] getBytes = s.getBytes();
        // **将字符串变成字符数组
        char[] toCharArray = s.toCharArray();
        // **返回指定索引出的字符
        char charAt = s.charAt(7);
        // **是否包含字符串"contains"
        boolean contains = s.contains("contains");
        // **将字符串s中的c全部替换为C
        String replaceAll = s.replaceAll("c", "C");
        // 将字符串中的1替换为一
        String replace = s.replace("1", "一");
        // **截取字符串s中的索引从0到3的字符
        String substring = s.substring(0, 3);
        // 截取字符串s中索引从4开始的字符
        String substring1 = s.substring(4);
        // 字符串s是否以6结尾
        boolean endsWith = s.endsWith("6");
        // 字符串是否以a开头
        boolean startsWith = s.startsWith("compareTo");
        // **将字符串s以字符c进行分割
        String[] split = s.split("c");
        // 将字符串s以字符c进行分割，分割成3份(如果最大能够分割到3份的话，如果最大不能分割到3份，则默认分割到最大份数)
        String[] split1 = s.split("c", 3);
        // 将字符串7890拼接到字符串s的后面，与+拼接字符串的区别是，+号左右的字符串都可以是null，而concat左右都不允许，否则会报空指针异常
        String concat = s.concat("7890");
        // 返回字符串是否相等，与equals区别，equals仅限于两个String类型字符串进行比较，而contentEquals可以比较类型为CharSequence的，
        // 而且如果比较的是StringBuffer还会加锁
        boolean contentEquals = s.contentEquals("contentEquals");
        // 比较两个字符串是否相等(忽略大小写)，
        boolean equalsIgnoreCase = s.equalsIgnoreCase("Abcdefg123456");
        // **比较两个字符串是否相等(不忽略大小写)
        boolean equals = s.equals("contentEquals");
        // 判断字符串是否为空
        boolean empty = s.isEmpty();
        // **获取字符串的长度
        int length = s.length();
        // **返回指定字符在字符串s中的索引，如果找不到返回-1
        int indexOf = s.indexOf("一");
        // 将字符串全部转换为小写
        String toLowerCase = s.toLowerCase();
        // 将字符串全部转换为大写
        String toUpperCase = s.toUpperCase();
        // 去除字符串前后的空格
        String trim = "  abc   ".trim();
        // 将指定数量的字符串(s,7890,AAA)以固定格式(,)进行拼接
        String join = String.join(",",s, "7890", "AAA");

        System.out.println("codePointAt = " + codePointAt);
        System.out.println("compareTo = " + compareTo);
        System.out.println("codePointBefore = " + codePointBefore);
        System.out.println("codePointCount = " + codePointCount);
        System.out.println("offsetByCodePoints = " + offsetByCodePoints);
        System.out.println("getBytes = " + Arrays.toString(getBytes));
        System.out.println("toCharArray = " + Arrays.toString(toCharArray));
        System.out.println("charAt = " + charAt);
        System.out.println("contains = " + contains);
        System.out.println("replaceAll = " + replaceAll);
        System.out.println("replace = " + replace);
        System.out.println("substring = " + substring);
        System.out.println("substring1 = " + substring1);
        System.out.println("endsWith = " + endsWith);
        System.out.println("startsWith = " + startsWith);
        System.out.println("split = " + Arrays.toString(split));
        System.out.println("split1 = " + Arrays.toString(split1));
        System.out.println("concat = " + concat);
        System.out.println("contentEquals = " + contentEquals);
        System.out.println("equalsIgnoreCase = " + equalsIgnoreCase);
        System.out.println("indexOf = " + indexOf);
        System.out.println("toLowerCase = " + toLowerCase);
        System.out.println("toUpperCase = " + toUpperCase);
        System.out.println("join = " + join);
        System.out.println("equals = " + equals);
        System.out.println("empty = " + empty);
        System.out.println("length = " + length);
        System.out.println("trim = " + trim);
    }
上述打印结果为:

codePointAt = 49
compareTo = 16
codePointBefore = 103
codePointCount = 3
offsetByCodePoints = 11
getBytes = [97, 98, 99, 100, 101, 102, 103, 49, 50, 51, 52, 53, 54]
toCharArray = [a, b, c, d, e, f, g, 1, 2, 3, 4, 5, 6]
charAt = 1
contains = false
replaceAll = abCdefg123456
replace = abcdefg一23456
substring = abc
substring1 = efg123456
endsWith = true
startsWith = false
split = [ab, defg123456]
split1 = [ab, defg123456]
concat = abcdefg1234567890
contentEquals = false
equalsIgnoreCase = true
indexOf = -1
toLowerCase = abcdefg123456
toUpperCase = ABCDEFG123456
join = abcdefg123456,7890,AAA
equals = false
empty = false
length = 13
trim = abc
以上为个人总结记录使用，希望能够帮助其他人，如有不足或错误欢迎大家指正。