Accounts having negative balances

Sd1/P/interest/V2/.gitignore

+/.settings
+/target
+/.classpath
+/.project

Sd1/P/interest/V2/pom.xml

+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>de.hdm-stuttgart.de.sd1</groupId>
+  <artifactId>interest</artifactId>
+  <version>0.0.1-SNAPSHOT</version>
+  <packaging>jar</packaging>
+
+  <name>V1</name>
+  <url>http://maven.apache.org</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <javadocDestdir>~/tmp</javadocDestdir>
+  </properties>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>2.3.2</version>
+        <configuration>
+          <source>1.8</source>
+          <target>1.8</target>
+        </configuration>
+      </plugin>
+      
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-javadoc-plugin</artifactId>
+        <version>2.9.1</version>
+        <configuration>
+          <linksource>true</linksource>
+          <!-- Setting destDir interferes with taglet class  -->
+          <additionalJOptions>
+            <additionalJOption>-d ${javadocDestdir}</additionalJOption>
+          </additionalJOptions>
+          
+          <taglets>
+            <taglet>
+              <tagletClass>de.hdm_stuttgart.de.sd1.taglet.HtmlExtensionTaglet</tagletClass>
+            </taglet>
+          </taglets>
+          <tagletpath>../../../../../../../ws/eclipse/HtmlExtensionTaglet/target/classes</tagletpath>
+        </configuration>
+      </plugin>
+    </plugins>
+    
+    <resources>
+      <resource>
+        <directory>src/main/java</directory>
+        <includes>
+          <include> **/*.properties</include>
+        </includes>
+      </resource>
+    </resources>
+  </build>
+  
+
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>3.8.1</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

Sd1/P/interest/V2/src/main/java/de/hdm_stuttgart/mi/sd1/interest/Account.java

+package de.hdm_stuttgart.mi.sd1.interest;
+
+/**
+ * Dealing with account balances and interest calculations.
+ * 
+ */
+public class Account {
+
+  private static double         
+  interestRate = 1.5,           // applied to positive balances
+  defaultInterestRate = 15.;    // applied to negative balances
+
+  private double balance;       // Balances apply per-account thus in contrast
+                                // "static" must not appear here.
+
+  /**
+   * Create a new account having a balance of 0.
+   */
+  public Account() {            // Default Constructor. This one has no parameters and
+    setBalance(0);              // thus creates an initially empty account. 
+  }
+
+  /**
+   * Create a new account having of given initial balance.
+   * 
+   * @param balance 
+   *           The account's initial balance.
+   */
+  public Account(double balance) {  // Non-default constructor creating an account
+    setBalance(balance);            // with (possibly) non-zero balance.
+  }
+
+  /**
+   * @return The account's current balance.
+   */
+  public double getBalance() {
+    return balance;
+  }
+  /**
+   * Setting a (possibly) new balance.
+   * 
+   * @param balance
+   *      The desired new balance value. If greater than 10000
+   *      a warning message is being issued and the accounts current value will be retained.
+   */
+  public void setBalance(double balance) {
+    if (balance <= 10000) {
+      this.balance = balance; // "this" required to resolve name shadowing conflict of formal
+                              // parameter name "double stand" with respect to Account.stand .
+    } else {
+      System.out.println("Balance" + balance + " exceeds " + 10000);
+    }
+  }
+  /**
+   * Setting the interest rate common to all accounts. This one
+   * will be applied to positive balances only. For handling
+   * negative balances see {{@link #setDefaultInterestRate(double)}.
+   * 
+   * @param interestRate The desired (global) interest rate.
+   */
+  public static void setInterestRate(double interestRate) {  
+    Account.interestRate = interestRate;                         
+  }
+  public static double getInterestRate() {
+    return interestRate;
+  }
+  
+  /**
+   * @return
+   *     the current default interest rate value.
+   */
+  public static double getDefaultInterestRate() {
+    return defaultInterestRate;
+  }
+
+  /**
+   * This interest rate will be applied to negative balances. In contrast
+   * {{@link #setInterestRate(double)} will handle positive balance values.
+   * 
+   * @param defaultInterestRate
+   *                         the desired default interest rate value.
+   */
+  public static void setDefaultInterestRate(double defaultInterestRate) {
+    Account.defaultInterestRate = defaultInterestRate;
+  }
+
+  /**
+   * <p>Adding the annual interest to the current balance according to:</p>
+   * <math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
+            <mrow>
+                <msub>
+                    <mi>balance</mi>
+                    <mi>1</mi>
+                </msub>
+                <mo>=</mo>
+                <mrow>
+                    <mi>balance</mi>
+                      <mrow>
+                          <mo>(</mo>
+                          <mrow>
+                              <mi>1</mi>
+                              <mo>+</mo>
+                              <mfrac>
+                                  <mi>interestRate</mi>
+                                  <mi>100</mi>
+                              </mfrac>
+                          </mrow>
+                          <mo>)</mo>
+                      </mrow>
+                </mrow>
+            </mrow>
+        </math>
+   * <p>Positive balances will receive the value of {{@link #setInterestRate(double)} whereas the
+   * calculation of negative  balances will be based on {{@link #setDefaultInterestRate(double)}.</p>
+   */
+  public void applyInterest() {
+    if (0 < balance) {
+      balance = balance * (1 + interestRate / 100);
+    } else if (balance < 0){
+      balance = balance * (1 + defaultInterestRate / 100);
+    }
+  }
+
+  /**
+   * <p>Adding the interest of several years to the current balance according to:</p>
+   * <math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
+            <mrow>
+                <msub>
+                    <mi>balance</mi>
+                    <mi>years</mi>
+                </msub>
+                <mo>=</mo>
+                <mrow>
+                    <mi>balance</mi>
+                    <msup>
+                        <mrow>
+                            <mo>(</mo>
+                            <mrow>
+                                <mi>1</mi>
+                                <mo>+</mo>
+                                <mfrac>
+                                    <mi>interestRate</mi>
+                                    <mi>100</mi>
+                                </mfrac>
+                            </mrow>
+                            <mo>)</mo>
+                        </mrow>
+                        <mi>years</mi>
+                    </msup>
+                </mrow>
+            </mrow>
+        </math>
+   *
+   *<p>Positive balances will receive the value of {{@link #setInterestRate(double)} whereas the
+   * calculation of negative  balances will be based on {{@link #setDefaultInterestRate(double)}.</p>
+   * 
+   * @param years
+   *             the given time period.
+   */
+  public void applyInterest(int years) {
+    if (0 < balance) {
+      balance = balance * Math.pow((1 + interestRate / 100), years) ;
+    } else if (balance < 0){
+      balance = balance * Math.pow((1 + defaultInterestRate / 100), years) ;
+    }
+  }
+
+  /**
+   * Calculate the expected annual interest without changing the account's balance.
+   * 
+   * @return
+   *       Annual interest to be expected 
+   */
+  public double getYearlyInterest() {
+    return balance * interestRate / 100;
+  }
+}
\ No newline at end of file

Sd1/P/interest/V2/src/main/java/de/hdm_stuttgart/mi/sd1/interest/App.java

+package de.hdm_stuttgart.mi.sd1.interest;
+
+
+/**
+ * Testing the simple account
+ *
+ */
+public class App {
+  public static void main(String[] args) {
+
+    Account account = new Account(20.); // Create a new instance of class Account 
+    
+    account.setBalance(100.);           // set account's balance
+    System.out.println("Balance:" + account.getBalance()); // Display account's balance
+    
+    Account.setInterestRate(1.0);       // Setting the global interest rate
+        
+    account.applyInterest(3);           // raise balance by three years compounded interest 
+    
+    System.out.println("balance:" + account.getBalance());  // Display account's balance again
+    
+    
+    Account.setInterestRate(15.);
+    account.setBalance(-1000.);           // You owe me something!
+    account.applyInterest(3);
+
+    System.out.println("balance:" + account.getBalance());  // Display account's balance again
+  }
+}

Sd1/P/interest/V2/src/test/java/de/hdm_stuttgart/mi/sd1/interest/AccountTest.java

+package de.hdm_stuttgart.mi.sd1.interest;
+
+import junit.framework.Test;
+import junit.framework.TestCase;
+import junit.framework.TestSuite;
+
+/**
+ * Unit test for simple App.
+ */
+public class AccountTest extends TestCase {
+  
+  /**
+   * @return the suite of tests being tested
+   */
+  public static Test suite() {
+    final TestSuite testsuite = new TestSuite("Testing accounts");
+    testsuite.addTestSuite(AccountTest.class);
+    return testsuite;
+  }
+
+  /**
+   * Testing account balance and interest calculatios
+   */
+  public void testApp() {
+    
+    Account account = new Account(20.); // Create a new instance of class Account 
+    
+    account.setBalance(100.);           // set account's balance
+    Account.setInterestRate(1.0);       // Setting the global interest rate
+    account.applyInterest();            // raise balance by one year's interest.
+    account.applyInterest(3);           // raise balance by three years compounded interest 
+ 
+    assertTrue(account.getBalance() == 104.06040100000001);
+
+    account.setBalance(-1000.);           // You owe me something!
+    account.applyInterest(3);
+    
+    assertTrue(account.getBalance() == -1520.8749999999998); 
+  
+  }
+}