5.6. Unit 4 Summary¶

In this chapter you learned about loops. Loops are used to repeat a statement or block of statements inside a pair of curly braces.

5.6.1. Concept Summary¶

Body of a Loop - The single statement or a block of statements that can be repeated (a loop may not execute at all if the condition is false to start with). In Java the body of the loop is either the first statement following a while or for loop is the body of the loop or a block of statements enclosed in { and }.
For Loop - A loop that has a header with 3 optional parts: initialization, condition, and change. It does the initialization one time before the body of the loop executes, executes the body of the loop if the condition is true, and executes the change after the body of the loop executes before checking the condition again.
Infinite Loop - A loop that never ends.
Loop - A way to repeat one or more statements in a program.
Nested Loop - One loop inside of another.
Out of Bounds error - A run-time error that occurs when you try to access past the end of a string or list in a loop.
Trace Code - Writing down the values of the variables and how they change each time the body of the loop executes.
While Loop - A loop that repeats while a Boolean expression is true.

5.6.2. Java Keyword Summary¶

while - used to start a while loop
for - used to start a for loop or a for each loop
System.out.println(variable) - used to print the value of the variable. This is useful in tracing the execution of code and when debugging.

5.6.3. Vocabulary Practice¶

4-6-1: Drag the definition from the left and drop it on the correct concept on the right. Click the "Check Me" button to see if you are correct

Review the summaries above.

a loop that repeats while a Boolean condition is true
while loop
a loop that has three parts: initialization, condition, and change
for loop
one loop inside of another
nested loop

4-6-2: Drag the definition from the left and drop it on the correct method on the right. Click the "Check Me" button to see if you are correct.

Review the summaries above.

the statement or block of statements following a loop header that is repeated
body of a loop
a loop that never ends
infinite loop
writing down the values of variables for each execution of the loop body
trace code

For more practice, see this Quizlet.

5.6.4. Common Mistakes¶

Forgetting to change the thing you are testing in a while loop and ending up with an infinite loop.
Getting the start and end conditions wrong on the for loop. This will often result in you getting an out of bounds error. An out of bounds error occurs when you try to access past the end of a string.
Jumping out of a loop too early by using one or more return statements inside of the loop.

Here is an example of a while loop that doesn’t ever change the value in the loop so it never ends. If you run it refresh the page to stop it. Fix it.

Fix the infinite loop so that it counts from 3 down to 1.

Here is an example of going past the bounds of a string. This code should double all but the first and last letter in message. Fix the code so that it doesn’t cause an out of bounds error.

Fix the test condition in the loop below so that it doesn’t cause an out of bounds error.

Here is an example of jumping out of a loop too early. The code below is intended to test if all of the letters in a string are in ascending order from left to right. But, it doesn’t work correctly. Can you fix it?

Fix the code below so it does not leave the loop too early. Try the CodeLens button to see what is going on. When should you return true or false?

public class Loop3
{
    public static boolean isInOrder(String check)
    {
        int pos = 0;
        while (pos < check.length() - 1)
        {
            String letter1 = check.substring(pos, pos + 1);
            String letter2 = check.substring(pos + 1, pos + 2);
            if (letter1.compareTo(letter2) < 0)
            {
                return true;
            }
            pos++;
        }
        return false;
    }

public static void main(String[] args)
    {
        System.out.println(isInOrder("abca") + " should return false");
        System.out.println(isInOrder("abc") + " should return true");
    }
}

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

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect = "false should return false\ntrue should return true";

boolean passed = getResults(expect, output, "Expected output");
        assertTrue(passed);
    }

@Test
    public void test2()
    {
        boolean output = Loop3.isInOrder("zxy");

boolean passed = output == false;
        getResults("false", output + "", "isInOrder(\"zxy\")", passed);
        assertTrue(passed);
    }
}

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