📅  最后修改于: 2020-09-26 06:01:44             🧑  作者: Mango
Java 字符串 charAt()方法返回给定索引号的char值。
索引号从0开始到n-1,其中n是字符串的长度。如果给定的索引号大于或等于此字符串长度或负数,则返回StringIndexOutOfBoundsException。
public char charAt(int index) {
if ((index < 0) || (index >= value.length)) {
throw new StringIndexOutOfBoundsException(index);
}
return value[index];
}
字符串 charAt()方法的签名如下:
public char charAt(int index)
index:索引号,以0开头
字符值
CharSequence接口,位于java.lang包内。
StringIndexOutOfBoundsException:如果index为负值或大于此字符串长度。
public class CharAtExample{
public static void main(String args[]){
String name="javatpoint";
char ch=name.charAt(4);//returns the char value at the 4th index
System.out.println(ch);
}}
输出:
t
让我们看一下传递更大索引值的charAt()方法的示例。在这种情况下,它将在运行时引发StringIndexOutOfBoundsException。
"public class CharAtExample{
public static void main(String args[]){
String name="javatpoint";
char ch=name.charAt(10);//returns the char value at the 10th index
System.out.println(ch);
}}
输出:
Exception in thread "main" java.lang.StringIndexOutOfBoundsException:
String index out of range: 10
at java.lang.String.charAt(String.java:658)
at CharAtExample.main(CharAtExample.java:4)
让我们看一个简单的示例,在该示例中,我们从提供的字符串中访问第一个和最后一个字符。
public class CharAtExample3 {
public static void main(String[] args) {
String str = "Welcome to Javatpoint portal";
int strLength = str.length();
// Fetching first character
System.out.println("Character at 0 index is: "+ str.charAt(0));
// The last Character is present at the string length-1 index
System.out.println("Character at last index is: "+ str.charAt(strLength-1));
}
}
输出:
Character at 0 index is: W
Character at last index is: l
让我们看一个示例,其中我们访问出现在奇数索引处的所有元素。
public class CharAtExample4 {
public static void main(String[] args) {
String str = "Welcome to Javatpoint portal";
for (int i=0; i<=str.length()-1; i++) {
if(i%2!=0) {
System.out.println("Char at "+i+" place "+str.charAt(i));
}
}
}
}
输出:
Char at 1 place e
Char at 3 place c
Char at 5 place m
Char at 7 place
Char at 9 place o
Char at 11 place J
Char at 13 place v
Char at 15 place t
Char at 17 place o
Char at 19 place n
Char at 21 place
Char at 23 place o
Char at 25 place t
Char at 27 place l
让我们看一个示例,其中我们在计算字符串字符的频率。
public class CharAtExample5 {
public static void main(String[] args) {
String str = "Welcome to Javatpoint portal";
int count = 0;
for (int i=0; i<=str.length()-1; i++) {
if(str.charAt(i) == 't') {
count++;
}
}
System.out.println("Frequency of t is: "+count);
}
}
输出:
Frequency of t is: 4