How to get the position of a character in a string in Java

To obtain the position of a character in a string in Java, you can use the indexOf() function.

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Function syntax:

indexOf() function has the following four forms:

• public int indexOf(int ch): Returns the index of the first occurrence of the specified character in the string. If there is no such character in this string, returns -1.

• public int indexOf(int ch, int fromIndex): Returns the index of the first occurrence of the specified character in the string starting from the fromIndex position, if there is no such occurrence in this string characters, returns -1.

• int indexOf(String str): Returns the index of the first occurrence of the specified character in the string. If there is no such character in this string, returns -1.

• int indexOf(String str, int fromIndex): Returns the index of the first occurrence of the specified character in the string starting from the fromIndex position, if there is no such occurrence in this string character, returns -1.

Parameter introduction:

• ch -- Character, Unicode encoding.

• fromIndex -- The index position where the search starts. The first character is 0, the second is 1, and so on.

• str -- The substring to search for.

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Code implementation:

public class Main {
    public static void main(String args[]) {
        String string = "aaa456ac";  
        //查找指定字符是在字符串中的下标。在则返回所在字符串下标；不在则返回-1.  
        System.out.println(string.indexOf("b")); // indexOf(String str); 返回结果：-1，"b"不存在  
 
        // 从第四个字符位置开始往后继续查找，包含当前位置  
        System.out.println(string.indexOf("a",3));//indexOf(String str, int fromIndex); 返回结果：6  
 
        //（与之前的差别：上面的参数是 String 类型，下面的参数是 int 类型）参考数据：a-97,b-98,c-99  
 
        // 从头开始查找是否存在指定的字符  
        System.out.println(string.indexOf(99));//indexOf(int ch)；返回结果：7  
        System.out.println(string.indexOf('c'));//indexOf(int ch)；返回结果：7  
 
        //从fromIndex查找ch，这个是字符型变量，不是字符串。字符a对应的数字就是97。  
        System.out.println(string.indexOf(97,3));//indexOf(int ch, int fromIndex); 返回结果：6  
        System.out.println(string.indexOf('a',3));//indexOf(int ch, int fromIndex); 返回结果：6  
    }}

Output result:

-1
6
7
7
6
6

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