字符串和数组

3.1 演示字符串操作的应用程序

//Demonstrating some String methods.
public class StringDemo
{
    public static void main(String args [])
    {
        String strOb1 = "First String";
        String strOb2 = "Second String";
        String StrOb3 = strOb1;
        System.out.println("Length of strOb1:" +strOb1.length ());
        System.out.println("Char at index 3 in strOb1:" +strOb1.charAt (3));
        if(strOb1.equals(strOb2))
            System.out.println("strOb1 == strOb2");
        else
            System.out.println("strOb1 ! = strOb2");
        if (strOb1.equals(strOb3))
            System.out.println("strOb1 == strOb3");
        else
            System.out.println("strOb1 != strOb3");
    }
}

运行出错，回头检查

Compilation Failed
/usercode/file.java:15: error: cannot find symbol
  if (strOb1.equals(strOb3))
                    ^
  symbol:   variable strOb3
  location: class file
1 error