Time estimate: 45 min.

2.4. Nested if Statements¶

If statements can be nested inside other if statements. Nested if statements consist of if, if-else, or if-else-if statements within if, if-else, or if-else-if statements. The Boolean expression of the inner nested if statement is evaluated only if the Boolean expression of the outer if statement evaluates to true.

if (boolean expression)
{   // This nested if is executed if outer if is true
    if (boolean expression)
    {
        statement;
    }
}

2.4.1. Multiway selection (else if)¶

A single if/else statement allows us to select between 2 branches of code. With nested if/else statements, we can pick between 3 or more branches of code. A multi-way selection (if-else-if) is used when there are a series of expressions with different segments of code for each condition. Multi-way selection is performed such that no more than one segment of code is executed based on the first expression that evaluates to true. If no expression evaluates to true and there is a trailing else statement, then the body of the else is executed.

Just add else if for each possibility after the first if, and else before the last possibility like below.

// 3 way choice with else if
if (boolean expression)
{
   statement1;
}
else if (boolean expression)
{
   statement2;
}
else
{
   statement3;
}

Coding Exercise

Run the code below and try changing the value of x to get each of the three possible lines in the conditional to print.

public class TryElseIf
{
    public static void main(String[] args)
    {
        int x = 2;
        if (x < 0)
        {
            System.out.println("x is negative");
        }
        else if (x == 0)
        {
            System.out.println("x is 0");
        }
        else
        {
            System.out.println("x is positive");
        }
        System.out.println("after conditional");
    }
}

====
 import static org.junit.Assert.*;
 import org.junit.*;
 import java.io.*;
 import java.util.regex.Pattern;
 import java.util.regex.Matcher;

public class RunestoneTests extends CodeTestHelper {
     public RunestoneTests() {
         super("TryElseIf"); // for Book
     }

@Test
     public void test01() {
         String code = getCode();
         String actual = "";
         int num = 2;

Pattern pattern = Pattern.compile("x\\s*=\\s*(-?\\d+)");
         Matcher matcher = pattern.matcher(code);
         if (matcher.find()) {
             actual = matcher.group();
         }

boolean passed = !stringMatch(code, "x = 2;");

getResults("x = ?;", actual, "Checking that x has been changed.", passed);
         assertTrue(passed);
     }

@Test
     public void test02() {
         String code = getCode();
         String actual = "";
         int num = 2;

Pattern pattern = Pattern.compile("x\\s*=\\s*(-?\\d+)");
         Matcher matcher = pattern.matcher(code);
         if (matcher.find()) {
             actual = matcher.group();
             //num = Integer.parseInt(matcher.group(1));
         }

boolean passed = actual.contains("-") || actual.contains("0");

getResults("x <= 0", actual, "Checking that x is zero or negative", passed);
         assertTrue(passed);
     }

@Test
     public void test03() {
         String output = getMethodOutput("main").split("\n")[0];
         String expect = "x is negative";

String code = getCode();
         String actual = "";
         int num = 2;

Pattern pattern = Pattern.compile("x\\s*=\\s*(-?\\d+)");
         Matcher matcher = pattern.matcher(code);
         if (matcher.find()) {
             actual = matcher.group();
             num = Integer.parseInt(matcher.group(1));
         }

if (num == 0) expect = "x is zero";

boolean passed = getResults(expect, output, "Checking for correct output");
         assertTrue(passed);
     }

private boolean stringMatch(String str1, String str2) {
         str1 = str1.replaceAll("\\s", "");
         str2 = str2.replaceAll("\\s", "");

return str1.contains(str2);
     }
 }

Here is a flowchart for a conditional with 3 options like in the code above.

../_images/Condition-three.png — Figure 1: The order that statements execute in a conditional with 3 options: if, else if, and else¶

Note

Another way to handle 3 or more conditional cases is to use the switch and break keywords, but these will not be on the exam. For a tutorial on using switch see https://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html.

Check your understanding

2-4-2: What does the following code print when x has been set to -5?

if (x < 0)
{
   System.out.println("x is negative");
}
else if (x == 0)
{
   System.out.println("x is zero");
}
else
{
   System.out.println("x is positive");
}

x is negative
When x is equal to -5 the condition of x < 0 is true.
x is zero
This will only print if x has been set to 0. Has it?
x is positive
This will only print if x is greater than zero. Is it?

2-4-3: What does the following code print when x has been set to 2000?

if (x < 0)
{
   System.out.println("x is negative");
}
else if (x == 0)
{
   System.out.println("x is zero");
}
else
{
   System.out.println("x is positive");
}

x is negative
This will only print if x has been set to a number less than zero. Has it?
x is zero
This will only print if x has been set to 0. Has it?
x is positive
The first condition is false and x is not equal to zero so the else will execute.

2-4-4: What does the following code print when x has been set to .8?

if (x < .25)
{
    System.out.println("first quartile");
}
else if (x < .5)
{
    System.out.println("second quartile");
}
else if (x < .75)
{
    System.out.println("third quartile");
}
else
{
    System.out.println("fourth quartile");
}

first quartile
This will only print if x is less than 0.25.
second quartile
This will only print if x is greater than or equal to 0.25 and less than 0.5.
third quartile
The first only print if x is greater than or equal to 0.5 and less than 0.75.
fourth quartile
This will print whenever x is greater than or equal to 0.75.

Coding Exercise

The else-if connection is necessary if you want to hook up conditionals together. In the following code, there are 4 separate if statements instead of the if-else-if pattern. Will this code print out the correct grade? First, trace through the code to see why it prints out the incorrect grade. Use the Code Lens button. Then, fix the code by adding in 3 else’s to connect the if statements and see if it works.

import java.util.Scanner;

public class IfDebug
 {
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        int score = scan.nextInt();
        String grade = "";

if (score >= 90)
        {
            grade = "A";
        }
        if (score >= 80)
        {
            grade = "B";
        }
        if (score >= 70)
        {
            grade = "C";
        }
        if (score >= 60)
        {
            grade = "D";
        }
        else
        {
            grade = "F";
        }

System.out.println(grade);
    }
}

====
 import static org.junit.Assert.*;
 import org.junit.*;
 import java.io.*;

public class RunestoneTests extends CodeTestHelper
 {

public RunestoneTests()
     {
         super("IfDebug"); // for Book
     }

private static String input1 = "93";

@Test
     public void test01()
     {
         //String input = input1.replaceAll(" ", "\n");
         String x = "95";
         String result = "A";
         String output = getMethodOutputWithInput("main", x);