如何检查特定字符串是否在另一个字符串中多次出现？

Question

我的代码从用户那里获取输入，如果有两个"bread"子字符串，则将打印它们之间的字符串。例如，"breadjavabread"输出"java"。但是，当我的代码只有一个"bread"字符串时，会弹出错误。例如，"usjdbbreaddudub"。我该如何解决？

String cheese = "no bread";
String bread = "bread";
for (int i = 0; i < s.length() - 5; i++)
{
  String m = s.substring(i, i + 5);
  if (m.equals(bread))
  {
    cheese = s.substring(s.indexOf(bread) + bread.length(), s.lastIndexOf(bread));
  }
}

System.out.print(cheese);

Answer 1

有很多方法可以解决此问题。这是其中的三个

1. 比较indexOf和lastIndexOf

   String cheese;
   String bread = "bread";
   int firstIndex = s.indexOf(bread);
   int lastIndex = s.lastIndexOf(bread);
   if (firstIndex == -1) {
       cheese = "no bread";
   } else if (lastIndex == firstIndex) {
       cheese = "only one bread";
   }
   cheese = s.substring(firstIndex + bread.length(), lastIndex);
   
   System.out.print(cheese);
   

2. 正则表达式：

   Matcher m = Pattern.compile("bread(.+?)bread").matcher(s);
   if (m.find()) {
       System.out.println(m.group(1));
   } else {
       System.out.println("Not enough bread");
   }
   

3. 拆分：

   String[] parts = s.split("bread");
   if (parts.length == 3) {
       System.out.println(parts[1]);
   } else {
       System.out.println("Not enough or too much bread");
   }