Because you can't assign a statement like that in Java. Your ternary would work if you used it like,
System.out.println(i%2==0 ? "even" : "odd");
Fundamentally, Java isn't C.
Edit
You ask in the comments, where am i assigning anything?
To quote Equality, Relational, and Conditional Operators (The Java Tutorials),
Another conditional operator is ?:, which can be thought of as shorthand for an if-then-else statement (discussed in the Control Flow Statements section of this lesson). This operator is also known as the ternary operator because it uses three operands. In the following example, this operator should be read as: "If someCondition is true, assign the value of value1 to result. Otherwise, assign the value of value2 to result."
Further, Chapter 15. Expressions - Conditional Operator ? : (JLS-15.25) says
It is a compile-time error for either the second or the third operand expression to be an invocation of a void method.
