String类下的contains()方法报错

Question

package cn.itcast_03;

/*

• 判断功能:
• boolean equals(Object obj):比较字符串的内容是否相同，区分大小写
• boolean equalsIgnoreCase(String str):比较字符串的内容是否相同，忽略大小写
• boolean contains(String str):判断大字符串中是否包含小字符串
• boolean startsWith(String str):判断字符串是否是否以某个指定的字符串开头
• boolean endsWith(String str):判断字符串是否以某个指定的字符串结尾
• boolean isEmpty():判断字符串是否为空。
• 注意:
• 字符串内容为空和字符串对象为空。
• String s = "";

•  String s = null;
  

  */
  public class StringDemo {
  public static void main(String[] args) {
  // 创建字符串对象
  String s1 = "helloworld";
  String s2 = "helloworld";
  String s3 = "Helloworld";

  // boolean equals(Object obj):比较字符串的内容是否相同，区分大小写
  System.out.println("equals:" + s1.equals(s2));
  System.out.println("equals:" + s1.equals(s3));
  System.out.println("--------------------");
  
  // boolean equalsIgnoreCase(String str):比较字符串的内容是否相同，忽略大小写
  System.out.println("equals:" + s1.equalsIgnoreCase(s2));
  System.out.println("equals:" + s1.equalsIgnoreCase(s3));
  System.out.println("--------------------");
  
  // boolean contains(String str):判断大字符串中是否包含小字符串
  System.out.println(s1.contains("hello"));//这行报错 
  

  }
  }

Exception in thread "main" java.lang.Error: Unresolved compilation problems:
The type java.lang.CharSequence cannot be resolved. It is indirectly referenced from required .class files
The method contains(CharSequence) from the type String refers to the missing type CharSequence

at cn.itcast_03.StringDemo.main(StringDemo.java:35)

Answer 1

我试了下你的代码没有问题，可以运行并得到正确结果。

修改看下是否是jdk的问题，http://blog.csdn.net/xl553488213/article/details/40512633