ch09 revisions

Author: ChrisMayfield

ch09/ArgValid.java

@@ -0,0 +1,20 @@
+/**
+ * Example of argument validation.
+ */
+public class ArgValid {
+
+    public static boolean isCapitalized(String str) {
+        if (str == null || str.isEmpty()) {
+            return false;
+        }
+        return Character.isUpperCase(str.charAt(0));
+    }
+
+    public static void main(String[] args) {
+        System.out.println(isCapitalized("Hi!"));
+        System.out.println(isCapitalized("bye"));
+        System.out.println(isCapitalized(""));
+        System.out.println(isCapitalized(null));
+    }
+
+}

ch09/BigInt.java

@@ -0,0 +1,20 @@
+import java.math.BigInteger;
+
+/**
+ * BigInteger examples.
+ */
+public class BigInt {
+
+    public static void main(String[] args) {
+        long x = 17;
+        BigInteger big = BigInteger.valueOf(x);
+
+        String s = "12345678901234567890";
+        BigInteger bigger = new BigInteger(s);
+
+        BigInteger a = BigInteger.valueOf(17);
+        BigInteger b = BigInteger.valueOf(1700000000);
+        BigInteger c = a.add(b);
+    }
+
+}

ch09/Objects.java

@@ -1,5 +1,3 @@
-import java.math.BigInteger;
-
 /**
  * Demonstrates uses of objects and wrappers.
  */
@@ -14,22 +12,40 @@ public static void main(String[] args) {
         char[] array = {'c', 'a', 't'};
         String word = "dog";
 
+        String word1 = new String("dog");  // creates a string object
+        String word2 = "dog";  // implicitly creates a string object
+        
+        // the null keyword
+
+        String name0 = null;
+        int[] combo = null;
+        // System.out.println(name0.length());  // NullPointerException
+        // System.out.println(combo[0]);        // NullPointerException
+
         // Strings are immutable
 
         String name = "Alan Turing";
         String upperName = name.toUpperCase();
 
+        name.toUpperCase();           // ignores the return value
+        System.out.println(name);
+        name = name.toUpperCase();    // references the new string
+        System.out.println(name);
+
         String text = "Computer Science is fun!";
         text = text.replace("Computer Science", "CS");
 
         // Wrapper classes
 
+        Integer i = Integer.valueOf(5);
+        System.out.println(i.equals(5));  // displays true
+
         Integer x = Integer.valueOf(123);
         Integer y = Integer.valueOf(123);
-        if (x == y) {                           // false
+        if (x == y) {                     // false
             System.out.println("x and y are the same object");
         }
-        if (x.equals(y)) {                      // true
+        if (x.equals(y)) {                // true
             System.out.println("x and y have the same value");
         }
 
@@ -38,18 +54,6 @@ public static void main(String[] args) {
 
         num = 12345;
         str = Integer.toString(num);
-
-        // BigInteger arithmetic
-
-        long z = 17;
-        BigInteger big = BigInteger.valueOf(z);
-
-        String s = "12345678901234567890";
-        BigInteger bigger = new BigInteger(s);
-
-        BigInteger a = BigInteger.valueOf(17);
-        BigInteger b = BigInteger.valueOf(1700000000);
-        BigInteger c = a.add(b);
     }
 
 }

ch09/Tables.java

@@ -4,73 +4,61 @@
 public class Tables {
 
     public static void printRow() {
-        int i = 1;
-        while (i <= 6) {
+        for (int i = 1; i <= 6; i++) {
             System.out.printf("%4d", 2 * i);
-            i = i + 1;
         }
         System.out.println();
     }
 
     public static void printRow(int n) {
-        int i = 1;
-        while (i <= 6) {
+        for (int i = 1; i <= 6; i++) {
             System.out.printf("%4d", n * i);  // generalized n
-            i = i + 1;
         }
         System.out.println();
     }
 
     public static void printTable() {
-        int i = 1;
-        while (i <= 6) {
+        for (int i = 1; i <= 6; i++) {
             printRow(i);
-            i = i + 1;
         }
     }
 
     public static void printTable(int rows) {
-        int i = 1;
-        while (i <= rows) {  // generalized rows
+        for (int i = 1; i <= rows; i++) {     // generalized rows
             printRow(i);
-            i = i + 1;
         }
     }
 
     public static void printRow(int n, int cols) {
-        int i = 1;
-        while (i <= cols) {  // generalized cols
+        for (int i = 1; i <= cols; i++) {     // generalized cols
             System.out.printf("%4d", n * i);
-            i = i + 1;
         }
         System.out.println();
     }
 
     public static void printTable2(int rows) {
-        int i = 1;
-        while (i <= rows) {
-            printRow(i, rows);  // added rows argument
-            i = i + 1;
+        for (int i = 1; i <= rows; i++) {
+            printRow(i, rows);
         }
     }
 
     public static void main(String[] args) {
-        System.out.println("printRow()");
+        System.out.println("\nprintRow()");
         printRow();
 
-        System.out.println("printRow(6)");
+        System.out.println("\nprintRow(6)");
         printRow(6);
 
-        System.out.println("printTable()");
+        System.out.println("\nprintTable()");
         printTable();
 
-        System.out.println("printTable(6)");
+        System.out.println("\nprintTable(6)");
         printTable(6);
 
-        System.out.println("printRow(6, 6)");
+        System.out.println("\nprintRow(6, 6)");
         printRow(6, 6);
 
-        System.out.println("printTable2(6)");
+        System.out.println("\nprintTable2(6)");
         printTable2(6);
     }