I got this question from a worksheet my AP Computer Science teacher had on his worksheet:
class Exam{
private int myA, myB;
private final int MAX = 100;
public Exam( ) { myA = myB = 100; }
public Exam ( int a, int b ) { myA = a; myB = b; }
public void setA(int a) { myA = a; }
public void setB(int b) { myB = b; }
public int getA() { return myA; }
public int getB() { return myB; }
public String toString( ) { return getA() + " " + getB(); }
}
How many accessor methods are in Exam?
Three are accessor methods. An accessor "accesses" the variable. Only three of them directly return the private variables. All of the others are mutators because they "mutate" the variables. The last accessor listed below is not a great accessor because it doesn't follow encapsulation best practices.
These are the accessors.
public int getA() { return myA; }
public int getB() { return myB; }
public String toString( ) { return getA() + " " + getB(); }
Related
I am still fairly new to java. I want to make a game with 3 character types that have different stats. I am using int values for each type so that their attack value is a range instead of just being a constant value. Since each character has a different range, I want to substitute an int value instead of an actual number for the method to get a random number. Here is my code.
package battleme;
import java.util.Random;
/**
*
* #author Kitten
*/
class Character {
String name;
int life;
int playerAttacklow;
int playerAttackhigh;
int playerDefense;
int playerLevel;
int currentXP;
int currentGold;
public Character(String name, int life, int playerAttacklow,
int playerAttachhigh, int playerDefense,
int playerLevel, int currentXP, int currentGold) {
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getLife() {
return life;
}
public void setLife(int life) {
this.life = life;
}
public int getPlayerAttacklow() {
return playerAttacklow;
}
public void setPlayerAttacklow(int playerAttacklow) {
this.playerAttacklow = playerAttacklow;
}
public int getPlayerAttackhigh() {
return playerAttackhigh;
}
public void setPlayerAttackhigh(int playerAttackhigh) {
this.playerAttackhigh = playerAttackhigh;
}
public int getPlayerDefense() {
return playerDefense;
}
public void setPlayerDefense(int playerDefense) {
this.playerDefense = playerDefense;
}
public int getPlayerLevel() {
return playerLevel;
}
public void setPlayerLevel(int playerLevel) {
this.playerLevel = playerLevel;
}
public int getCurrentXP() {
return currentXP;
}
public void setCurrentXP(int currentXP) {
this.currentXP = currentXP;
}
public int getCurrentGold() {
return currentGold;
}
public void setCurrentGold(int currentGold) {
this.currentGold = currentGold;
}
//the problem child
int ActualAttackGen(int playerAttackhigh, int playerAttacklow) {
Random rn = new Random();
int randomNum;
randomNum= rn.nextInt((playerAttackhigh-playerAttacklow) + 1)+ playerAttacklow ;
return randomNum ;
}
package battleme;
public class BattleMe {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here
Character Warrior = new Character("Warrior", 30, 2, 10, 3, 1, 1, 15);
Character Rouge = new Character("Rouge", 25, 3, 6, 2, 1, 1, 15);
Character Mage = new Character("Mage", 18, 2, 8, 1, 1, 1, 15);
// trying to run the problem child
System.out.println(Warrior.ActualAttackGen(Warrior.playerAttackhigh,Warrior.playerAttacklow));
}
}
Whenever I try to run this, I always get an value of 0. Please help!
In your constructor you have to assign the passed values to the respective member of your Character class:
public Character(String name, int life, int playerAttacklow,
int playerAttachhigh, int playerDefense,
int playerLevel, int currentXP, int currentGold) {
this.name = name;
....
}
BTW: It would be good coding practice to distinguish member and parameter names. Usually one prefixes one of them (or both). E.g. member myName, parameter aName. So you do not have to reference the member with "this.":
myName = aName;
I have the following test example:
var a = new List<OrderRule> {
new OrderRule("name", OrderDirection.Ascending),
new OrderRule("age", OrderDirection.Descending)
};
var b = new List<OrderRule> {
new OrderRule("name", OrderDirection.Ascending),
new OrderRule("age", OrderDirection.Descending)
};
var r = a.SequenceEqual(b);
Assert.Equal(a, b);
The variable r is true but Assert.Equal is false ...
The OrderRule class is the following:
public class OrderRule : IEquatable<OrderRule> {
public OrderDirection Direction { get; }
public String Property { get; }
public OrderRule(String property, OrderDirection direction) {
Direction = direction;
Property = property;
}
public Boolean Equals(OrderRule other) {
if (other == null)
return false;
return Property.Equals(other.Property) && Direction.Equals(other.Direction);
}
public override Boolean Equals(Object obj) {
if (ReferenceEquals(null, obj))
return false;
if (ReferenceEquals(this, obj))
return true;
if (obj.GetType() != GetType())
return false;
return Equals(obj as IncludeRule);
}
public override Int32 GetHashCode() {
return HashCode.Of(Property).And(Direction);
}
}
public enum OrderDirection { ASC, DESC }
Is there any problem with Assert.Equal when overriding Equals and implementing IEquatable?
UPDATE - HashCode helper
public struct HashCode {
private readonly Int32 Value;
private HashCode(Int32 value) {
Value = value;
}
public static implicit operator Int32(HashCode hashCode) {
return hashCode.Value;
}
public static HashCode Of<T>(T item) {
return new HashCode(GetHashCode(item));
}
public HashCode And<T>(T item) {
return new HashCode(CombineHashCodes(Value, GetHashCode(item)));
}
public HashCode AndEach<T>(IEnumerable<T> items) {
Int32 hashCode = items.Select(x => GetHashCode(x)).Aggregate((x, y) => CombineHashCodes(x, y));
return new HashCode(CombineHashCodes(Value, hashCode));
}
private static Int32 CombineHashCodes(Int32 x, Int32 y) {
unchecked {
return ((x << 5) + x) ^ y;
}
}
private static Int32 GetHashCode<T>(T item) {
return item == null ? 0 : item.GetHashCode();
}
}
Your code works as expected on my side. I've only fixed compilation erros - IncludeRule changed to OrderRule in Equals, also fixed OrderDirection enum members.
I have to implement this method:
public int GetAverage(Node root){
//TODO implement
}
this method should get average value of all nodes of root tree. where :
public interface Node {
int getValue();
List<Node> getNodes();
}
do you have any ideas how to implement this method?
thank you
my attempt:
public static double value;
public static int count;
public static double getAverage(Node root) {
count++;
value += root.getValue();
for (Node node : root.getNodes()) {
getAverage(node);
}
return value / count;
}
but how to do it without the static fields outside of the method?
Simply traverse through all nodes and remember the count and the overall sum of all values. Then calculate the average. This is an example written in Java.
public interface INode {
int getValue();
List<INode> getNodes();
}
public class Node implements INode {
private List<INode> children = new ArrayList<INode>();
private int value;
#Override
public int getValue() {
return value;
}
#Override
public List<INode> getNodes() {
return children;
}
public static int getAverage(INode root) {
if (root == null)
return 0;
Counter c = new Counter();
calculateAverage(root, c);
return c.sum / c.count;
}
class Counter {
public int sum;
public int count;
}
private static void calculateAverage(INode root, Counter counter) {
if (root == null)
return;
counter.sum += root.getValue();
counter.count++;
// recursively through all children
for (INode child : root.getNodes())
calculateAverage(child, counter);
}
}
public static double getAverage(Node root) {
Pair p = new Pair(0,0);
algo(root, p);
return ((double) p.element1) / ((double) p.element2);
}
private static void algo(Node root, Pair acc) {
for(Node child : root.getNodes()) {
algo(child, acc);
}
acc.sum += root.getValue();
acc.nbNodes++;
}
With Pair defined as follows:
public class Pair {
public int sum;
public int nbNodes;
public Pair(int elt1, int elt2) {
this.sum = elt1;
this.nbNodes = elt2;
}
}
I am a newbie to Trident and I'm looking to create an 'Average' aggregator similar to 'Sum(), but for 'Average'.The following does not work:
public class Average implements CombinerAggregator<Long>.......{
public Long init(TridentTuple tuple)
{
(Long)tuple.getValue(0);
}
public Long Combine(long val1,long val2){
return val1+val2/2;
}
public Long zero(){
return 0L;
}
}
It may not be exactly syntactically correct, but that's the idea. Please help if you can. Given 2 tuples with values [2,4,1] and [2,2,5] and fields 'a','b' and 'c' and doing an average on field 'b' should return '3'. I'm not entirely sure how init() and zero() work.
Thank you so much for your help in advance.
Eli
public class Average implements CombinerAggregator<Number> {
int count = 0;
double sum = 0;
#Override
public Double init(final TridentTuple tuple) {
this.count++;
if (!(tuple.getValue(0) instanceof Double)) {
double d = ((Number) tuple.getValue(0)).doubleValue();
this.sum += d;
return d;
}
this.sum += (Double) tuple.getValue(0);
return (Double) tuple.getValue(0);
}
#Override
public Double combine(final Number val1, final Number val2) {
return this.sum / this.count;
}
#Override
public Double zero() {
this.sum = 0;
this.count = 0;
return 0D;
}
}
I am a complete newbie when it comes to Trident as well, and so I'm not entirely if the following will work. But it might:
public class AvgAgg extends BaseAggregator<AvgState> {
static class AvgState {
long count = 0;
long total = 0;
double getAverage() {
return total/count;
}
}
public AvgState init(Object batchId, TridentCollector collector) {
return new AvgState();
}
public void aggregate(AvgState state, TridentTuple tuple, TridentCollector collector) {
state.count++;
state.total++;
}
public void complete(AvgState state, TridentCollector collector) {
collector.emit(new Values(state.getAverage()));
}
}
I am trying to implement the following in a Raw Comparator but not sure how to write this?
the tumestamp field here is of tyoe LongWritable.
if (this.getNaturalKey().compareTo(o.getNaturalKey()) != 0) {
return this.getNaturalKey().compareTo(o.getNaturalKey());
} else if (this.timeStamp != o.timeStamp) {
return timeStamp.compareTo(o.timeStamp);
} else {
return 0;
}
I found a hint here, but not sure how do I implement this dealing with a LongWritabel type?
http://my.safaribooksonline.com/book/databases/hadoop/9780596521974/serialization/id3548156
Thanks for your help
Let say i have a CompositeKey that represents a pair of (String stockSymbol, long timestamp).
We can do a primary grouping pass on the stockSymbol field to get all of the data of one type together, and then our "secondary sort" during the shuffle phase uses the timestamp long member to sort the timeseries points so that they arrive at the reducer partitioned and in sorted order.
public class CompositeKey implements WritableComparable<CompositeKey> {
// natural key is (stockSymbol)
// composite key is a pair (stockSymbol, timestamp)
private String stockSymbol;
private long timestamp;
......//Getter setter omiited for clarity here
#Override
public void readFields(DataInput in) throws IOException {
this.stockSymbol = in.readUTF();
this.timestamp = in.readLong();
}
#Override
public void write(DataOutput out) throws IOException {
out.writeUTF(this.stockSymbol);
out.writeLong(this.timestamp);
}
#Override
public int compareTo(CompositeKey other) {
if (this.stockSymbol.compareTo(other.stockSymbol) != 0) {
return this.stockSymbol.compareTo(other.stockSymbol);
}
else if (this.timestamp != other.timestamp) {
return timestamp < other.timestamp ? -1 : 1;
}
else {
return 0;
}
}
Now the CompositeKey comparator would be:
public class CompositeKeyComparator extends WritableComparator {
protected CompositeKeyComparator() {
super(CompositeKey.class, true);
}
#Override
public int compare(WritableComparable wc1, WritableComparable wc2) {
CompositeKey ck1 = (CompositeKey) wc1;
CompositeKey ck2 = (CompositeKey) wc2;
int comparison = ck1.getStockSymbol().compareTo(ck2.getStockSymbol());
if (comparison == 0) {
// stock symbols are equal here
if (ck1.getTimestamp() == ck2.getTimestamp()) {
return 0;
}
else if (ck1.getTimestamp() < ck2.getTimestamp()) {
return -1;
}
else {
return 1;
}
}
else {
return comparison;
}
}
}
Are you asking about way to compare LongWritable type provided by hadoop ?
If yes, then the answer is to use compare() method. For more details, scroll down here.
The best way to correctly implement RawComparator is to extend WritableComparator and override compare() method. The WritableComparator is very good written, so you can easily understand it.
It is already implemented from what I see in the LongWritable class:
/** A Comparator optimized for LongWritable. */
public static class Comparator extends WritableComparator {
public Comparator() {
super(LongWritable.class);
}
public int compare(byte[] b1, int s1, int l1,
byte[] b2, int s2, int l2) {
long thisValue = readLong(b1, s1);
long thatValue = readLong(b2, s2);
return (thisValue<thatValue ? -1 : (thisValue==thatValue ? 0 : 1));
}
}
That byte comparision is the override of the RawComparator.