Java Sting charAt方法

Java String charAt(int index)方法返回字符串中指定索引处的字符。我们在此方法中传递的索引值应介于 0 和(string的长度 -1)之间。例如:s.charAt(0)将返回实例s表示的字符串的第一个字符。如果在charAt()方法中传递的索引值小于 0 或大于等于字符串的长度(index < 0 || index >= length()),则 Java String charAt方法抛出IndexOutOfBoundsException

Java String charAt()方法示例

让我们举一个例子来理解charAt()方法的使用。在这个例子中,我们有一个字符串,我们使用charAt()方法打印字符串的第 1,第 6,第 12 和第 21 个字符。

public class CharAtExample {
   public static void main(String args[]) {
    String str = "Welcome to string handling tutorial";
    //This will return the first char of the string
    char ch1 = str.charAt(0);

    //This will return the 6th char of the string
    char ch2 = str.charAt(5);

    //This will return the 12th char of the string
    char ch3 = str.charAt(11);

    //This will return the 21st char of the string
    char ch4 = str.charAt(20);

    System.out.println("Character at 0 index is: "+ch1);
    System.out.println("Character at 5th index is: "+ch2);
    System.out.println("Character at 11th index is: "+ch3);
    System.out.println("Character at 20th index is: "+ch4);
   }
}

输出:

Character at 0 index is: W
Character at 5th index is: m
Character at 11th index is: s
Character at 20th index is: n

IndexOutOfBoundsException

当我们传递负索引或大于length() - 1的索引时,charAt()方法抛出IndexOutOfBoundsException。在下面的示例中,我们在charAt()方法中传递负索引,让我们看看我们在输出中得到了什么。

public class JavaExample {
   public static void main(String args[]) {
    String str = "BeginnersBook";
    //negative index, method would throw exception
    char ch = str.charAt(-1);
    System.out.println(ch);
   }
}

输出:

Java Sting charAt()方法

示例打印字符串的所有字符

为了打印字符串的所有字符,我们运行for循环从 0 到字符串的长度 -1,并使用charAt()方法在循环的每次迭代中显示字符。

public class JavaExample {
   public static void main(String args[]) {
    String str = "BeginnersBook";
    for(int i=0; i<=str.length()-1; i++) {
        System.out.println(str.charAt(i));
    }
   }
}

输出:

B
e
g
i
n
n
e
r
s
B
o
o
k

示例计算字符的出现次数

在此示例中,我们将使用charAt()方法计算给定字符串中特定字符的出现次数。这里我们有一个字符串,我们正在计算字符串中字符'B'的出现次数。

public class JavaExample {
   public static void main(String[] args) {  
        String str = "BeginnersBook"; 

        //initialized the counter to 0
        int counter = 0;  

        for (int i=0; i<=str.length()-1; i++) {  
            if(str.charAt(i) == 'B') { 
                //increasing the counter value at each occurrence of 'B'
                counter++;  
            }  
        }  
        System.out.println("Char 'B' occurred "+counter+" times in the string");  
   }  
}

输出:

Java Sting charAt()方法

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