"if-then" Statements

Java Tutorials - Herong's Tutorial Examples

∟"if-then" Statements

This section describes 'if-then' statement, which is a decision-making statement that executes contained sub-statements only when the given 'boolean' expression is 'true'.

"if" statements have 2 forms: "if-then" statements and "if-then-else" statements. Let's look at "if-then" statements in this tutorial first.

What Is "if-then" Statement? - An "if-then" statement is a decision-making statement that executes the contained sub-statement only when the given "boolean" expression is "true".

Here is the syntax for an "if-then" statement. Note that "then" is not used a keyword used in the statement at all.

if (condition_expression) contained_statement

The contained sub-statement can be a simple single statement, or a complex statement block. Here is a sample program that shows you how to use "if-then" statements:

/* IfThenStatementTest.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
class IfThenStatementTest {
   public static void main(String[] arg) {
      java.io.PrintStream out = System.out;

      out.println("\"if-then\" statement containing a single statement:");
      boolean isNewYear = true;
      if (isNewYear) out.println("   Happy New Year!");

      out.println("\"if-then\" statement containing a statement block:");
      boolean hasError = true;
      if (hasError) {
         out.println("   Open the log file.");
         out.println("   Write an error message.");
         out.println("   Close the log file.");
      }
   }
}

If you compile and run the above program, you will see:

herong> java IfElseStatementTest.java

"if-then" statement containing a single statement:
   Happy New Year!
"if-then" statement containing a statement block:
   Open the log file.
   Write an error message.
   Close the log file.