問題描述：在字符串中尋找特定字符

1、第1次出現位置

實現函數原型： int indexOf(char c)

Java代碼：

import java.io.*;
public class Way_1
{public static void main(String args[]){String str = "Geeks for Geeks is a computer science portal";System.out.println(str.length());int firstIndex = str.indexOf('s');System.out.println("First occurrence of char 's' is found at: " + firstIndex);int firstIn = str.indexOf('z');System.out.println("First occurrence of char 'z' is found at: " + firstIn);        }
}

樣例字符串： Geeks for Geeks is a computer science portal

樣例輸出：

2、最后一次出現位置

實現函數原型： public int lastIndexOf(char c)

Java代碼：

import java.io.*;
public class Way_2
{public static void main(String args[]){String str = "Geeks for Geeks is a computer science portal";System.out.println(str.length());int lastIndex = str.lastIndexOf('s');System.out.println("Last occurrence of char 's' is found at: " + lastIndex);			int lastIn = str.lastIndexOf('z');System.out.println("Last occurrence of char 'z' is found at: " + lastIn);        }
}

樣例字符串： Geeks for Geeks is a computer science portal

樣例輸出：

3、指定位置后的首次出現

實現函數原型： public int IndexOf(char c, int indexFrom)

說明： 除-1外，該函數的返回值必然大于或等于其第2個參數indexFrom。

Java代碼：

import java.io.*;public class String_Search
{public static void main(String [] args){String str = "Geeks For Geeks is a computer  science portal";System.out.println(str.length());int first_in = str.indexOf('s', 10);System.out.println("First occurrence of char 's' after index 10: " + first_in);int first_not_in = str.indexOf('z', 10);System.out.println("First occurrence of char 'z' after index 10: " + first_not_in);}
}

樣例字符串： Geeks For Geeks is a computer science portal

樣例輸出：

4、指定位置前的末次出現

實現函數原型： public int lastIndexOf(char c, int fromIndex)

說明： 除-1外，該函數的返回值必然小于或等于其第2個參數fromIndex。

Java代碼：

import java.io.*;public class String_Search_2
{public static void main(String [] args){String str = "Geeks For Geeks is a computer science portal";System.out.println(str.length());int lastIndex = str.lastIndexOf('s', 20);System.out.println("Last occurrence of char 's' before index 20: " + lastIndex);int last_not_in = str.lastIndexOf('z', 20);System.out.println("Last occurrence of char 'z' before index 20: " + last_not_in);}
}

樣例字符串： Geeks For Geeks is a computer science portal

樣例輸出：

5、指定位置的字符

實現函數原型： char charAt(int indexNumber)

說明： 若指定的下標indexNumber超出字符串長度范圍，則拋出StringIndexOutOfBounds異常。

Java代碼：

import java.io.*;public class Character_At
{public static void main(String [] args){String str = "Geeks For Geeks is a computer science portal";System.out.println(str.length());int char_at = str.charAt(20);System.out.println("Character at location 20: " + char_at);int char_not_at = str.charAt(60);}
}

樣例字符串： Geeks For Geeks is a computer science portal

樣例輸出：