3.13. Coding Practice

Write the code to print a random number from 1 to 100. You can use Math.random() to get a value between 0 and not quite 1.

public class Test1 { public static void main(String[] args) {} } ==== import static org.junit.Assert.*; import org.junit.*; import java.io.*; public class RunestoneTests extends CodeTestHelper { @Test public void testCheckCodeContains1() { boolean passed = checkCodeContainsNoRegex("random number up to 100", "Math.random()*100"); assertTrue(passed); } @Test public void testCheckCodeContains2() { boolean passed = checkCodeContainsNoRegex("random number starting at 1", "+1"); assertTrue(passed); } @Test public void testCheckCodeContains3() { boolean passed = checkCodeContains("casting to int", "(int)"); assertTrue(passed); } }

First multiply the output from Math.random() times 100 and then cast it to an integer. This will result in a random number from 0 to 99. Add one to make it from 1 to 100.

Answer: This is the answer to the previous question.

public class Test1 { public static void main(String[] args) { System.out.println(((int) (Math.random() * 100)) + 1); } }

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The following code should get the first letter of the first name, middle name, and last name and append (concatenate) them together and then return them all in lowercase. However, the code has errors. Fix the code so that it compiles and runs correctly.

public class Test1 { public static void main(String[] args) { String firstName = "Sofia'; String middleName = "Maria"; String lastName "Hernandez"; String initials = firstname.substring(0,1) + middleName.subString(0,1) + lastName.substring(0,1); System.out.println(initials.toLowerCase(); } } ==== import static org.junit.Assert.*; import org.junit.*; import java.io.*; public class RunestoneTests extends CodeTestHelper { @Test public void testMain() throws IOException { String output = getMethodOutput("main"); String expect = "smh"; boolean passed = getResults(expect, output, "Expected output from main"); assertTrue(passed); } @Test public void testCodeContains() { String target = ".substring(0,1)"; boolean passed = checkCodeContains("substring method", target); assertTrue(passed); } }

Line 5 has an ending ' instead of ". Line 7 is missing a =. Line 8 has firstname, but it should be firstName. Remember that you should uppercase the first letter of each new word, after the first word, to make the variable name easier to read (use camel case). Line 9 has subString, but the method name is substring. Line 11 is missing a ).

Answer: This is the answer to the previous question.

public class Test1 { public static void main(String[] args) { String firstName = "Sofia"; String middleName = "Maria"; String lastName = "Hernandez"; String initials = firstName.substring(0, 1) + middleName.substring(0, 1) + lastName.substring(0, 1); System.out.println(initials.toLowerCase()); } }

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The following code should print the first 3 letters of the string message all in lowercase letters. However, the code has errors. Fix the errors so that the code runs as intended.

public class Test1 { public static void main(String[] args) { String message = "Meet me by the bridge": String part = message.substring(1,3); String lower = message.toLowerCase(); System.println(lower); } } ==== import static org.junit.Assert.*; import org.junit.*; import java.io.*; public class RunestoneTests extends CodeTestHelper { @Test public void testMain() throws IOException { String output = getMethodOutput("main"); String expect = "mee"; boolean passed = output.equals(expect); passed = getResults(expect, output, "Expected output from main", passed); assertTrue(passed); } @Test public void testCodeContains() { String target = ".substring(0,3)"; boolean passed = checkCodeContains("substring method ", target); assertTrue(passed); } }

Line 5 ends with : when it should be ;. Line 6 should be substring(0,3). Line 7 should be part not message. Line 8 should be System.out.println.

This is the answer to the previous question.

public class Test1 { public static void main(String[] args) { String message = "Meet me by the bridge"; String part = message.substring(0, 3); String lower = part.toLowerCase(); System.out.println(lower); } }

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The following code starts with String name1 = ALEX; and should print Alex. Use the toLowerCase and substring methods to do this task.

public class Test1 { public static void main(String[] args) { String name1 = "ALEX"; System.out.println(name1); } } ==== import static org.junit.Assert.*; import org.junit.*; import java.io.*; public class RunestoneTests extends CodeTestHelper { @Test public void testMain() throws IOException { String output = getMethodOutput("main"); String expect = "Alex"; boolean passed = getResults(expect, output, "Expected output from main"); assertTrue(passed); } @Test public void testCodeContains() { String target = ".substring("; boolean passed = checkCodeContains("substring method", target); assertTrue(passed); } }

Create a string that is all lowercase. Create a new string from a substring of the original string (first letter) and a substring of the rest of the string that is all lowercase (all except the first letter). Print that string.

This is the answer to the previous question.

public class Test1 { public static void main(String[] args) { String name1 = "ALEX"; String nameLower = name1.toLowerCase(); String finalName = name1.substring(0, 1) + nameLower.substring(1); System.out.println(finalName); } }

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The following code should remove the word “very “ (and following space) from the message and print the new message. You can use indexOf to find the position of a substring in your string. You can use substring to create a new string removing the word.

public class Test1 { public static void main(String[] args) { String message = "I am very happy!"; String target = "very "; } } ==== import static org.junit.Assert.*; import org.junit.*; import java.io.*; public class RunestoneTests extends CodeTestHelper { @Test public void testMain() throws IOException { String output = getMethodOutput("main"); String expect = "I am happy!"; boolean passed = getResults(expect, output, "Expected output from main"); assertTrue(passed); } @Test public void testCodeContains() { String target = ".substring("; boolean passed = checkCodeContains("substring method", target); assertTrue(passed); } @Test public void testCodeContains2() { String target = ".indexOf("; boolean passed = checkCodeContains("indexOf method", target); assertTrue(passed); } }

Use indexOf to find the position and then create a new message up to the pos and again after the target string.

This is the answer to the previous question.

public class Test1 { public static void main(String[] args) { String message = "I am very happy!"; String target = "very "; int pos = message.indexOf(target); String newMessage = message.substring(0, pos) + message.substring(pos + target.length()); System.out.println(newMessage); } }

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The following code should replace lol in the message with laugh out loud and print the new message using indexOf and substring.

public class Test1 { public static void main(String[] args) { String message = "That was great - lol."; } } ==== import static org.junit.Assert.*; import org.junit.*; import java.io.*; public class RunestoneTests extends CodeTestHelper { @Test public void testMain() throws IOException { String output = getMethodOutput("main"); String expect = "That was great - laugh out loud"; boolean passed = getResults(expect, output, "Expected output from main"); assertTrue(passed); } @Test public void testCodeContains() { String target = ".substring("; boolean passed = checkCodeContains("substring method", target); assertTrue(passed); } @Test public void testCodeContains2() { String target = ".indexOf("; boolean passed = checkCodeContains("indexOf method", target); assertTrue(passed); } }

Use indexOf to find the position of the “lol” then create a new string from up to that position and append the “laugh out loud” and the substring after it.

This is the answer to the previous question.

public class Test1 { public static void main(String[] args) { String message = "That was great - lol."; String target = "lol"; int pos = message.indexOf(target); String newMessage = message.substring(0, pos) + "laugh out loud" + message.substring(pos + target.length()); System.out.println(newMessage); } }

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For more practice with Strings see problems at http://codingbat.com/java/String-1.

• http://codingbat.com/prob/p161056

• http://codingbat.com/prob/p147483

• http://codingbat.com/prob/p108853

• http://codingbat.com/prob/p130896

• http://codingbat.com/prob/p130781

Here are some practice coding problems for Turtles.

Finish the code below to have t1 draw a triangle where all of the sides are length 50.

import java.awt.*; import java.util.*; public class TurtleTest { public static void main(String[] args) { World habitat = new World(300, 300); Turtle t1 = new Turtle(habitat); habitat.show(true); } }

Finish the code below to have t1 draw a rectangle. The vertical sides should be length 50 and the horizontal length 100.

import java.awt.*; import java.util.*; public class TurtleTest { public static void main(String[] args) { World habitat = new World(300, 300); Turtle t1 = new Turtle(habitat); habitat.show(true); } }

Finish the code below to have t1 draw the number seven.

import java.util.*; import java.awt.*; public class TurtleTest { public static void main(String[] args) { World habitat = new World(300,300); Turtle t1 = new Turtle(habitat); habitat.show(true); } }

Finish the code below to have t1 draw the number four.

import java.awt.*; import java.util.*; public class TurtleTest { public static void main(String[] args) { World habitat = new World(300, 300); Turtle t1 = new Turtle(habitat); habitat.show(true); } }

Finish the code below to have t1 draw something interesting.

import java.awt.*; import java.util.*; public class TurtleTest { public static void main(String[] args) { World habitat = new World(300, 300); Turtle t1 = new Turtle(habitat); habitat.show(true); } }

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