java.lang.String.indexOf()方法

package com.yiibai;

import java.lang.*;

public class StringDemo {

  public static void main(String[] args) {
  
    String str = "This is yiibai";
    
    // returns the index of occurrence of character s
    System.out.println("index of letter 's' = " + str.indexOf('s')); 
      
    // returns -1 as character e is not in the string
    System.out.println("index of letter 'e' = " + str.indexOf('e'));
  }
}

经过编译：

index of letter 's' = 3
index of letter 'e' = -1