Java Relational Operators

4 Key excerpts on "Java Relational Operators"

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  eBook - ePub

  Computer Programming for Beginners

  A Step-By-Step Guide

  • Murali Chemuturi(Author)
  • 2018(Publication Date)
  • Chapman and Hall/CRC

    (Publisher)

  6.  Whenever a division operator is used in the expression, we need to ensure that the denominator does not become zero. So, before programming an arithmetic expression, we need to check and ensure that the denominator is not zero. We can do this using control statements and relational expressions. I would suggest programming the division operation on a separate line by itself.

  Relational Expressions

  Relational expressions relate one expression with another and determine if the relationship between the two is true or false. Relational expressions are used for decision making and are used in control statements. They are not used in assignment statements. The expressions in the relational expressions are joined together by the relational operators. Relational operators specify the type of relation to be established between both the expressions. The relational operators are given in Table 7.1 .

  While parentheses are not relational operators, parentheses are often used to enclose a relational expression. It is a good practice of programming to enclose the entire relational expression in a set of parentheses. The relational operators given in Table 7.1 are the popular representation used by most programming languages. But variations can be seen in some programming languages. For example, COBOL uses full text, such as LESS THAN, GREATER THAN, NOT EQUAL, and so on. In some programming languages, the characters le, ge, eq, and so on, are used. You need to check the programming language manual or help pages to know exactly what relational operators are used in that language.

  As noted earlier in this chapter, an expression can contain a variable, or a constant, or a combination of variables and constants. We need to follow the following rules when writing relational expressions:

  1.  The expressions need to be on different sides of a relational operator. The relational operator would be in the middle with one expression on its left-hand side and the other expression would be on its right-hand side.

  2.  A relational expression can contain only one relational operator. We cannot have more than one relational operator in a relational expression.

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  eBook - ePub

  Java

  The Comprehensive Guide

  • Christian Ullenboom(Author)
  • 2022(Publication Date)
  • SAP PRESS

    (Publisher)

  90 , 0 }; int j = 0 ; array2[++ j ] += 10 ; System. out . println ( Arrays . toString ( array2 ) ); // [0, 100, 0]

  2.4.6     Relational Operators and Equality Operators

  Relational operators are comparison operators that compare expressions with each other, and the result is a truth value of the boolean type. The operators provided by Java for numerical comparisons include the following:

  • Greater than ( > )
  • Less than ( < )
  • Greater than or equal to ( ⩾ )
  • Less than or equal to ( ⩽ )

  The special operator instanceof is for testing type relationships.

  In addition, two comparison operators , called equality operators , are available in Java:

  • Test for equality ( == )
  • Test for inequality ( != )

  The fact that Java makes a distinction between equality operators and comparison operators is due to a slightly different precedence, but this order of precedence shouldn’t concern you any further.

  Like arithmetic operators, relational operators match their operands to a common type. If the types are reference types, only the comparison operators == and != are allowed. An exception is string , where + is also allowed.

  Confusion Caused by == and =

  The use of the relational operator == and the assignment operator = often causes problems for beginners because mathematics always knows only one equal sign for comparisons and assignments. Fortunately, the problem in Java isn’t as drastic as in C(++), for example, because the types of the operators are different. The comparison operator always returns only the boolean

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  eBook - ePub

  Beginning Java Programming

  The Object-Oriented Approach

  • Bart Baesens, Aimee Backiel, Seppe vanden Broucke(Authors)
  • 2015(Publication Date)
  • Wrox

    (Publisher)

  switch is an alternative structure that’s similar to an if-then statement, but offers a list of cases that can be defined so each is handled differently or so groups of cases can be handled the same. Finally, you’ll learn about some keywords that have specific uses in guiding the execution of a program.

  COMPARISONS USING OPERATORS AND METHODS

  You have already seen operators, such as arithmetic operators, in Chapter 2. Operators are based on mathematical concepts and many will look familiar, even to those unfamiliar with programming. This chapter discusses two types of control operators, comparative and logical, that are used frequently in control structures. The syntax for operators will differ whether the data type is primitive or composite. Recall that primitive types include char , boolean , and many numeric representations, like int , double , and float . Arrays, strings, and other defined classes are composite data types.

  Comparing Primitive Data Types with Comparison Operators

  Given the importance of operators when defining control structures, this section briefly revisits some of the underlying concepts covered in Chapter 2.

  For primitive data types, there are well-defined operators, as outlined in Table 5.1 , which can be used to compare the values of two variables. Equality and relational comparison operators compare the values of two operands for equality, inequality, greater than, or less than. The result of these expressions is a Boolean true or false . With primitive types, the following expressions are used for comparison:

  • Equal: ==
  • Not equal: !=
  • Greater than: >
  • Greater than or equal: >=
  • Less than: <
  • Less than or equal: <=

  Table 5.1

  Control Operators for Primitive Data Types

  OPERATOR	JAVA SYNTAX	ENGLISH EQUIVALENT
  Equality	x == y x != y	Is x equal to y ? Is x not equal to y ?
  Relational	x < y x <= y x > y x >= y	Is x less than y ? Is x less than or equal to y ? Is x greater than y ? Is x greater than or equal to y ?
  Logical	x && y x || y !x	Are x and y both true? Is x , y , or both true? Is x false?

  Note that the ! indicates negation. While these operators are used for most primitive data types, there is an exception; Boolean operands can only be compared with equality operators and not with relational operators. That is, true cannot be greater than or less than false ; however, true can be equal to true

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  eBook - PDF

  Information Modeling and Relational Databases

  From Conceptual Analysis to Logical Design

  • Terry Halpin(Author)
  • 2001(Publication Date)
  • Morgan Kaufmann

    (Publisher)

  Now let’s begin with relational algebra. In the relational model of data, all facts are stored in tables (or relations). New tables may be formed from existing tables by applying operations in the relational algebra. The tables resulting from these operations may be named and stored, using relational assignment. The original relational algebra defined by Codd contained eight relational operators: four based on traditional set operations (union, intersection, difference, and Cartesian product) and four special operations (selection, projection, join, and divi-sion). Each of these eight relational operators is a table-forming operator on tables. For example, the union of two tables is itself a table. Relational algebra includes six comparison operators ( = , <> , < , > , <= , >= ). These are proposition-forming operators on terms. For example, x <> 0 asserts that x is not equal to zero. It also includes three logical operators (and, or, not). These are proposition-forming operators on propositions (e.g., x > 0 and x < 8). Since the alge-bra does not include arithmetic operators (e.g., + ) or functions (e.g., count), it is less expressive than SQL. Proposed extensions to the algebra to include these and other op-erators are ignored here. Many different notations exist for expressing the relational algebra. A comparison between our notation and a common academic notation is given later. To simplify dis-cussion, I’ll often use informal terms instead of the strict relational terminology (e.g., “table” and “row” instead of “relation” and “tuple”). Union, Intersection, and Difference Two tables are union-compatible if and only if they have the same number of columns, and their corresponding columns are based on the same domain (the columns may have different names). Treating a table as a set of rows, the traditional set operations of union, intersection, and difference may be defined between tables that are union-compatible.

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