2.12. Coding Practice¶

The coding problems below are mostly about Strings, but more problems on other topics in this unit will be added in the future.

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.

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.

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);
      }
  }

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.

The following code starts with String name1 = ALEX; and should print Alex. Use the toLowerCase and substring methods to assign the variable finalName to the value Alex.

public class Test1
{
    public static void main(String[] args)
    {
        String name1 = "ALEX";
        String finalName;

System.out.println(finalName);
    }
}
====
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);
      }
      @Test
      public void testCodeContains2()
      {
          String target = ".toLowerCase(";
          boolean passed = checkCodeContains("toLowerCase method", target);
          assertTrue(passed);
      }
  }

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);
      }
  }

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

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

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