How to make if statement true if variable doesn't match a list of values in Java?

Question

I'm trying to create a boolean condition for an if statement where it's true if the variable exactly matches any of the following strings, but I keep getting this error:

error: bad operand types for binary operator '||'

My code at the moment is:

if(pProvince != ("Alberta"||"British Columbia"||"Manitoba"||"New Brunswick"||"Newfoundland And Labrador"||"Nova Scotia"||"Ontario"||"Prince Edward Island"||"Quebec"||"Saskatchewan"||"Northern Territories"||"Nunavut"||"Yukon")){
    //do stuff
}else{
    //do other stuff
}

Any suggestions? I'm fairly new to java programming so don't be afraid to lecture me on how to use boolean operators properly.

Answer 1

don't be afraid to lecture me on how to use boolean operators properly

<cracks knuckles>

The most basic thing to know is that boolean operators take boolean operands (an operand is an argument you pass to an operator).

So, in !A, the operand A has to be something whose type is boolean (or Boolean); and in A || B, both operands A and B have to be things whose type is boolean (or Boolean).

In "Alberta" || "BC", you're trying to give the || boolean operator string operands. This is what it's complaining about.

You need to create a boolean expressions based on the string, e.g.

pProvince.equals("Alberta")  // this is either true or false.

or

pProvince.equals("BC")  // again, either true or false.

and then combine those that with a boolean operator, e.g.

pProvince.equals("BC") || pProvince.equals("Alberta")  // still either true or false

and then, if you want, use other binary operators such as !, e.g.

!(pProvince.equals("BC") || pProvince.equals("Alberta"))  // even now! either true or false

---

However, there are other, better ways of checking a string against multiple strings.

In this case, I would create a set of strings:

Set<String> provinces = Set.of("Alberta", "BC");

and then check using provinces.contains(pProvince). Actually, you could use any kind of Collection instead of a Set, e.g. a List. However, Set is the most appropriate if all you're doing is invoking contains, because that can be done more efficiently for implementations of Set such as a HashSet (O(1) time) or TreeSet (O(log N) time).

Another way could be to use a switch statement:

switch (pProvince) {
  case "Alberta":
  case "BC":
  // ... other provinces
    //do other stuff
    break;

  default:
    //do stuff
}

Another option could be to use regular expressions.

Answer 2

Instead of this, use collection. Declare Set and then add all these values to it. Use set.contains for comparison

Set<String> provinces=new HashSet<>();

provinces.add("Alberta");
provinces.add("British Columbia");

if(provinces.contains(pProvince)) {
//Matched
}

This solution will give you result in O(1)

Answer 3

In java you can not use '||' directly inside parentheses to compare. you can do it only this way.

if (!(pProvince.equals("Alberta") || pProvince.equals("British Columbia") || pProvince.equals("Manitoba") || pProvince.equals("New Brunswick") || pProvince.equals("Newfoundland And Labrador") || pProvince.equals("Nova Scotia") || pProvince.equals("Ontario") || pProvince.equals("Prince Edward Island") || pProvince.equals("Quebec") || pProvince.equals("Saskatchewan") || pProvince.equals("Northern Territories") || pProvince.equals("Nunavut") || pProvince.equals("Yukon"))) {
    // do stuff
} else {
    // do other stuff
}

which is not readable. I suggest you create a List of strings and then check if value contains like:

List<String> provinces = Arrays.asList(
    "Alberta", "British Columbia", "Manitoba", "New Brunswick", "Newfoundland And Labrador",
    "Nova Scotia", "Ontario", "Prince Edward Island", "Quebec", "Saskatchewan",
    "Northern Territories", "Nunavut", "Yukon"
);

if (!provinces.contains(pProvince)) {
    // do stuff
} else {
    // do other stuff
}

Answer 4

You could try: pProvince.equals("Alberta") then you get a true or false as result, but its only for one. You can use a string array for all the names and you can check all the names step by step with a "for next loop"

Answer 5

In Java, to compare String values, use the String.equals method.

boolean value = pProvince.equals("Alberta");

Since you're looking to match a set of values, there are a few approaches for this.

You can create a method which will return a boolean if the argument matches a set of values within an array.

boolean matches(String string) {
    String[] strings = {
        "Alberta", "British Columbia", "Manitoba", "New Brunswick",
        "Newfoundland And Labrador", "Nova Scotia", "Ontario",
        "Prince Edward Island", "Quebec", "Saskatchewan",
        "Northern Territories", "Nunavut", "Yukon"
    };
    for (String value : strings) 
        if (value.equals(string)) return true;
    return false;
}

Another approach, if you're familiar with regular expressions, is the String.matches method, which takes a regular expression pattern as the parameter.

boolean matches(String string) {
    String regex = 
        "Alberta|British Columbia|Manitoba|New Brunswick|" +
        "Newfoundland And Labrador|Nova Scotia|Ontario|" +
        "Prince Edward Island|Quebec|Saskatchewan|" +
        "Northern Territories|Nunavut|Yukon";
    return string.matches(regex);
}

Answer 6

The error message you're seeing suggests that the operands used with the '||' (logical OR) operator in your if statement are not valid. In Java, the '||' operator expects Boolean values (true or false) as operands, rather than strings. To perform string matching in an if statement, you can use the '==' operator with brackets '( ... )' and the '=' operator for pattern matching. Here's an example of how you can check if a variable exactly matches any of the specified strings:

Code:

variable="example"

if ( variable == "string1" || variable == "string2" || variable == "string3" ){ 
  //do stuff
}else{
  //do stuff}

Replace "string1", "string2", and "string3" with the strings you want to match against your variable.