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13.1: Relational Operators

  • Page ID
    15235
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    Relational operators are used to check conditions like whether two values are equal, or whether one is greater than the other. The following expressions show how they are used:

    x == y          // x is equal to y
    x != y          // x is not equal to y
    x > y           // x is greater than y
    x < y           // x is less than y
    x >= y          // x is greater than or equal to y
    x <= y          // x is less than or equal to y
    

    The result of a relational operator is one of two special values, true or false. These values belong to the data type boolean; in fact, they are the only boolean values.

    You are probably familiar with these operations, but notice that the Java operators are different from the mathematical symbols like =, ≠, and ≤. A common error is to use a single = instead of a double ==. Remember that = is the assignment operator, and == is a comparison operator. Also, there is no such thing as the =< or => operators.

    The two sides of a relational operator have to be compatible. For example, the expression 5 < "6" is invalid because 5 is an int and "6" is a String. When comparing values of different numeric types, Java applies the same conversion rules we saw previously with the assignment operator. For example, when evaluating the expression 5 < 6.0, Java automatically converts the 5 to 5.0.

    Most relational operators don’t work with strings. But confusingly, == and != do work with strings – they just don’t do what you expect. We’ll explain what they do later; in the meantime, don’t use them with strings. Instead, you should use the equals method:

    String fruit1 = "Apple";
    String fruit2 = "Orange";
    System.out.println(fruit1.equals(fruit2));
    

    The result of fruit1.equals(fruit2) is the boolean value false.


    13.1: Relational Operators is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .

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