String常用 方法

1、length()：获取字符串长度

String str1 = "abcde fghij";
int len = str1.length();
System.out.println(len);  //返回11

2、charAt()：获取某个字符

String str1 = "abcde fghij";
char c = str1.charAt(3);
System.out.println(c);  //返回字符d

3、 toCharArray()：将字符串变成一个字符数组

String str1 = "abcde fghij";
char[] c = str1.toCharArray();
System.out.println(c);  //返回字符数组abcde fghij
System.out.println(c[3]);  //返回字符d

3、concat() ：连接两个字符串

String str1 = "abcde fghij";
String str2 = " abcde EGHIJ";

String str3 = str1.concat(str2);
System.out.println(str3);  //返回abcde fghij abcde EGHIJ

4、trim()：去掉起始和结束的空格

String str1 = "    abcde fghij    ";
System.out.println(str1);  //返回"    abcde fghij    "

String str3 = str1.trim();
System.out.println(str3);  //返回"abcde fghij"

5、substring()：截取字符串

String str1 = "abcde fghij";
String str2 = str1.substring(3);

String str3 = str1.substring(4,7);
System.out.println(str2);  //返回"de fghij"
System.out.println(str3);  //返回"e f"

6、replace() 替换

String str1 = "abcde abcde";
String str2 = "你好";

String str3 = str1.replace('a','A');
String str4 = str1.replace("de","DE");
String str5 = str2.replace("你","大家");

System.out.println(str3);  //返回"Abcde Abcde"
System.out.println(str4);  //返回"abcDE abcDE"
System.out.println(str5);  //返回"大家好"

7、equals()和equalsIgnoreCase()比较两个字符串是否相等，前者区分大小写，后者不区分

String str1 = "abcde fghij";
String str2 = "abcde FGHIJ";

System.out.println(str1.equals(str2));  //返回false
System.out.println(str1.equalsIgnoreCase(str2));  //返回true

8、startsWith()和endsWith()：判断字符串是不是以特定的字符开头或结束

String str1 = "abcde FGHIJ";

System.out.println(str1.startsWith("bc"));  //返回false
System.out.println(str1.endsWith("IJ"));  //返回true

9、toUpperCase()和toLowerCase()：将字符串转换为大写或小写

String str1 = "abcde FGHIJ";
String str2 = str1.toLowerCase();
String str3 = str1.toUpperCase();
System.out.println(str2);  //返回abcde fghij
System.out.println(str3);  //返回ABCDE FGHIJ

10、indexOf()和lastIndexOf()前者是查找字符或字符串第一次出现的地方，后者是查找字符或字符串最后一次出现的地方，没有则返回-1

String str1 = "abcde fgbcj";
int n1 = str1.indexOf("bc");
int n2 = str1.lastIndexOf("bc");
int n3 = str1.indexOf("dd");
System.out.println(n1);  //返回1
System.out.println(n2);  //返回8
System.out.println(n3);  //返回-1

11、compareTo()和compareToIgnoreCase(）按字典顺序比较两个字符串的大小，前者区分大小写，后者不区分，从左往右返回第一个不相同字符的asc码的差值

String str1 = "abcde fghij";
String str2 = "abcde EGHIJ";
int n1 = str1.compareTo(str2);
int n2 = str1.compareToIgnoreCase(str2);
System.out.println(n1);  //返回33（f-E=102-69），asc码，e：101,f:102，E：69
System.out.println(n2);  //返回1（f-e=102-101）

12、split()：按照某个字符分解字符串

String str1 = "abc#de f*ghi&j";
String[] str3 = str1.split("#");

for(String st:str3){
System.out.println(st);
//输出：str3[0]=abc
//str[1]=de f*ghi&j
}