Ternary operator to return value- Java/Android

问题:

Just switched to Java from php

I encountered following issue

I want to rewrite

if(usrname.equals(username) && (passwd.equals(password))){
    return true;
}
else{
    return false;
}

as

(usrname.equals(username) && passwd.equals(password) )? return true : return false;

it is not working(syntax error) however,

int a=1;
int b=2;
int minVal = a < b ? a : b;

is working

Why ternary operator are not behaving correctly while returning value depending on some condition

EDIT

return  (usrname.equals(username) && passwd.equals(password)); 

could be solution if it return boolean .

lets say i need

 (usrname.equals(username) && passwd.equals(password) )? return "member": return "guest";

回答1:

You can do

return (usrname.equals(username) && passwd.equals(password) )?  true : false;

true and false can be replaced by any return value you want. If it is just boolean then you can avoid ternary operator altogether. Just do

return  (usrname.equals(username) && passwd.equals(password));

回答2:

lets say I need

  (usrname.equals(u) && passwd.equals(p)) ? return "member" : return guest";

The correct syntax is:

   return (usrname.equals(u) && passwd.equals(p)) ? "member" : "guest";

---

The general form of the ternary operator is

   expression-1 ? expression-2 : expression-3

where expression-1 has type boolean, and expression-2 and expression-3 have the same type¹.

In your code, you were using return statements where expressions are required. In Java, a return statement is NOT a valid expression.

^{1 - This doesn't take account of the conversions that can take. For the full story, refer to the JLS.}

---

Having said that, the best way to write your example doesn't uses the conditional operator at all:

   return usrname.equals(username) && passwd.equals(password);

回答3:

Why redundant boolean

Just use

return  (usrname.equals(username) && passwd.equals(password));

回答4:

By the way you can simplify:

return (usrname.equals(username) && passwd.equals(password) )? return true : return false;

To:

return usrname.equals(username) && passwd.equals(password);

The ternary operator work similar in php than Java, I think you have made a silly mistake, maybe "username" have a space or another white character

String a1 = "a";
String b1 = "b";

String a2 = "a";
String b2 = "b";

System.out.println((a1.equals(a2)&&b1.equals(b2))?"true":"false");

it return "true"

回答5:

Java ternary operator is an expression, and is thus evaluated to a single value. As per the Javadocs, for below given expression

result = someCondition ? value1 : value2;

if the boolean condition is true then assign the value of value1 to the result, else assign value2 to the result. Both value1 and value2 should be of same value type.

Hence the correct syntax of a return statement would be

return boolean_condition ? value_when_true : value_when_false