为啥结果不对？

HelloWorld.java

public class HelloWorld{  

  public static void main(String[] args) {  

      int a=16;      

     double b=9.5;        

     String str1="hello";    

     String str2="imooc";       

     System.out.println("a等于b：" + (a  == b));    

     System.out.println("a大于b：" + (a >  b));  

     System.out.println("a小于等于b：" + (a <=  b)); 

      System.out.println("str1等于str2：" + (str1  == str2));   

 }

}

error: ')' expected
System.out.println("a??b?" + (a b));
^
error: ';' expected
System.out.println("a??b?" + (a b));
^
error: ')' expected
System.out.println("a????b?" + (a b));
^
error: ';' expected
System.out.println("a????b?" + (a b));
^
error: ')' expected
System.out.println("str1??str2?" + (str1 str2));
^
error: ';' expected
System.out.println("str1??str2?" + (str1 str2));
^
6 errors