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-rw-r--r--java.html.markdown101
1 files changed, 91 insertions, 10 deletions
diff --git a/java.html.markdown b/java.html.markdown
index c2c1a18b..74140120 100644
--- a/java.html.markdown
+++ b/java.html.markdown
@@ -7,6 +7,7 @@ contributors:
- ["Simon Morgan", "http://sjm.io/"]
- ["Zachary Ferguson", "http://github.com/zfergus2"]
- ["Cameron Schermerhorn", "http://github.com/cschermerhorn"]
+ - ["Rachel Stiyer", "https://github.com/rstiyer"]
filename: LearnJava.java
---
@@ -127,7 +128,7 @@ public class LearnJava {
//
// BigInteger can be initialized using an array of bytes or a string.
- BigInteger fooBigInteger = new BigDecimal(fooByteArray);
+ BigInteger fooBigInteger = new BigInteger(fooByteArray);
// BigDecimal - Immutable, arbitrary-precision signed decimal number
@@ -137,13 +138,18 @@ public class LearnJava {
//
// BigDecimal allows the programmer complete control over decimal
// rounding. It is recommended to use BigDecimal with currency values
- // and where exact decimal percision is required.
+ // and where exact decimal precision is required.
//
// BigDecimal can be initialized with an int, long, double or String
// or by initializing the unscaled value (BigInteger) and scale (int).
BigDecimal fooBigDecimal = new BigDecimal(fooBigInteger, fooInt);
-
+
+ // Be wary of the constructor that takes a float or double as
+ // the inaccuracy of the float/double will be copied in BigDecimal.
+ // Prefer the String constructor when you need an exact value.
+
+ BigDecimal tenCents = new BigDecimal("0.1");
// Strings
@@ -184,8 +190,12 @@ public class LearnJava {
// LinkedLists - Implementation of doubly-linked list. All of the
// operations perform as could be expected for a
// doubly-linked list.
- // Maps - A set of objects that maps keys to values. A map cannot
- // contain duplicate keys; each key can map to at most one value.
+ // Maps - A set of objects that map keys to values. Map is
+ // an interface and therefore cannot be instantiated.
+ // The type of keys and values contained in a Map must
+ // be specified upon instantiation of the implementing
+ // class. Each key may map to only one corresponding value,
+ // and each key may appear only once (no duplicates).
// HashMaps - This class uses a hashtable to implement the Map
// interface. This allows the execution time of basic
// operations, such as get and insert element, to remain
@@ -202,8 +212,8 @@ public class LearnJava {
System.out.println("1+2 = " + (i1 + i2)); // => 3
System.out.println("2-1 = " + (i2 - i1)); // => 1
System.out.println("2*1 = " + (i2 * i1)); // => 2
- System.out.println("1/2 = " + (i1 / i2)); // => 0 (0.5 truncated down)
- System.out.println("1/2 = " + (i1 / (i2*1.0))); // => 0.5
+ System.out.println("1/2 = " + (i1 / i2)); // => 0 (int/int returns an int)
+ System.out.println("1/2 = " + (i1 / (double)i2)); // => 0.5
// Modulo
System.out.println("11%3 = "+(11 % 3)); // => 2
@@ -411,7 +421,7 @@ public class LearnJava {
// easier way, by using something that is called Double Brace
// Initialization.
- private static final Set<String> COUNTRIES = HashSet<String>() {{
+ private static final Set<String> COUNTRIES = new HashSet<String>() {{
add("DENMARK");
add("SWEDEN");
add("FINLAND");
@@ -445,6 +455,17 @@ class Bicycle {
protected int gear; // Protected: Accessible from the class and subclasses
String name; // default: Only accessible from within this package
+ static String className; // Static class variable
+
+ // Static block
+ // Java has no implementation of static constructors, but
+ // has a static block that can be used to initialize class variables
+ // (static variables).
+ // This block will be called when the class is loaded.
+ static {
+ className = "Bicycle";
+ }
+
// Constructors are a way of creating classes
// This is a constructor
public Bicycle() {
@@ -514,7 +535,7 @@ class PennyFarthing extends Bicycle {
// (Penny Farthings are those bicycles with the big front wheel.
// They have no gears.)
- public PennyFarthing(int startCadence, int startSpeed){
+ public PennyFarthing(int startCadence, int startSpeed) {
// Call the parent constructor with super
super(startCadence, startSpeed, 0, "PennyFarthing");
}
@@ -681,6 +702,66 @@ public abstract class Mammal()
return true;
}
}
+
+
+// Enum Type
+//
+// An enum type is a special data type that enables for a variable to be a set
+// of predefined constants. The variable must be equal to one of the values that
+// have been predefined for it. Because they are constants, the names of an enum
+// type's fields are in uppercase letters. In the Java programming language, you
+// define an enum type by using the enum keyword. For example, you would specify
+// a days-of-the-week enum type as:
+
+public enum Day {
+ SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
+ THURSDAY, FRIDAY, SATURDAY
+}
+
+// We can use our enum Day like that:
+
+public class EnumTest {
+
+ // Variable Enum
+ Day day;
+
+ public EnumTest(Day day) {
+ this.day = day;
+ }
+
+ public void tellItLikeItIs() {
+ switch (day) {
+ case MONDAY:
+ System.out.println("Mondays are bad.");
+ break;
+
+ case FRIDAY:
+ System.out.println("Fridays are better.");
+ break;
+
+ case SATURDAY:
+ case SUNDAY:
+ System.out.println("Weekends are best.");
+ break;
+
+ default:
+ System.out.println("Midweek days are so-so.");
+ break;
+ }
+ }
+
+ public static void main(String[] args) {
+ EnumTest firstDay = new EnumTest(Day.MONDAY);
+ firstDay.tellItLikeItIs(); // => Mondays are bad.
+ EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
+ thirdDay.tellItLikeItIs(); // => Midweek days are so-so.
+ }
+}
+
+// Enum types are much more powerful than we show above.
+// The enum body can include methods and other fields.
+// You can se more at https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html
+
```
## Further Reading
@@ -704,7 +785,7 @@ The links provided here below are just to get an understanding of the topic, fee
* [Generics](http://docs.oracle.com/javase/tutorial/java/generics/index.html)
-* [Java Code Conventions](http://www.oracle.com/technetwork/java/codeconv-138413.html)
+* [Java Code Conventions](http://www.oracle.com/technetwork/java/codeconvtoc-136057.html)
**Online Practice and Tutorials**