去掉字符串首尾空格
String str = " abcdefg ";
str = str.trim();
求字符串长度
String str = "abcdefg";
int length = str.length();
返回单个字符的位置
String str = "abcdefg";
System.out.println(str.indexOf("a"));
String str = "abcdefg";
System.out.println(str.indexOf(str, 1));
String str = "abcdefg";
System.out.println(str.lastIndexOf(str));
String str = "abcdefg";
System.out.println(str.lastIndexOf(str, 1));
字符串大小写转换
String str = "abcdefg";
str1 = str.toUpperCase();
str2 = str.toLowerCase();
获取字符串的子字符串
String str = "abcdefg";
int start = 0;
int end = str.length();
str = str.substring(start, end);
字符串字串的替换
String str = "abcdefg";
str = str.replaceAll("abc", "xyz");
字符串拼接
String str1 = "abc";
String str2 = "def";
System.out.println(str1+str2);
获取字符串中的某个字符
String str = "abcdefg";
int i = 0;
char c = str.charAt(i);
将字符串转为整数
String str = "123";
int num = Integer.parseInt(str);
System.out.println(num);