I am trying to convert an integer to a binary number string, and I wrote the code for it and it compiled. However, I can't seem to write a test file for it, i keep getting an error. I am supposed to write a separate test file that outputs my answer, however I am not sure how to do that. I'm pretty new to Java. Can anyone help me figure out how to fix the error I get?
This is my java code for to convert it.
public String binaryNumber( int j)
{
String n = "";
String a = "";
do
{
a += (j % 2);
j = j/2;
}while (j != 0);
for(int r = (a.length() - 1); r >=0; r--)
{
n += a.charAt(r);
}
return n;
}
public String getN {return n;}
This is my test code :
public class BinaryNumberTest
{
public static void main(String[] args)
{
System.out.println("Result: " + binaryNumber(45));
}
}
Your code seems correct if you make the binaryNumber(int j) method static. Because you can't access non-static method inside static context.
However you can use Integer.toBinaryString(x) to perform the task easily. Additionally, you can use Integer.toString(x,8) to convert octal, Integer.toString(x,2) to convert binary, Integer.toString(x,16) to convert hexa-decimal, and Integer.toString(x,n) to n base.
You should make your binaryNumber method static because you are not using instance fields.
public class BinaryNumber
{
public static String binaryNumber( int j)
{
String n = "";
String a = "";
do
{
a += (j % 2);
j = j/2;
}while (j != 0);
for(int r = (a.length() - 1); r >=0; r--)
{
n += a.charAt(r);
}
return n;
}
}
To test:
public class BinaryNumberTest
{
public static void main(String[] args)
{
System.out.println("Result: " + BinaryNumber.binaryNumber(45));
}
}
First, since binaryNumber doesn't use any instance members it could (read: should) be defined as static. Second, you need to reference it by its class name, or statically import it:
System.out.println("Result: " + BinaryNumber.binaryNumber(45));
Related
I know that the variable maxreps isn't in the scope of my main method so I wanted it call it by creating an object, but it still isn't able to get maxreps.
How could I fix this?
public class LUIS{
public void james(){
int current=1;
int maxreps=1;
String adriana = "aabbddddnsspkrrgg";
for(int a=0; a<adriana.length(); a++){
if(adriana.charAt(a) == adriana.charAt(a+1)){
current++;
if(maxreps>=current){
maxreps=current;
}
}
}
}
public static void main(String[] args){
LUIS fritz = new LUIS();
final int drei = fritz.james;
System.out.println(maxreps);
}
}
As you noted, scoping prevents seeing a variable defined in a different scope. You can resolve your particular issue by returning the value
public int james(){ // <-- change from void to an int return
int current=1;
int maxreps=1;
String adriana = "aabbddddnsspkrrgg";
for(int a=0; a<adriana.length(); a++){
if(adriana.charAt(a) == adriana.charAt(a+1)){
current++;
if(maxreps>=current){
maxreps=current;
}
}
}
return maxreps; // <-- return the value
}
And then in the main method set a variable to the returned value.
Alternatively, you can define it as a class variable, but there are reasons to avoid doing so -- globals are generally bad.
1) final int drei = fritz.james; cannot compile. You cannot invoke a method in this way (that is without ()).
2) Besides, the james() method should have a more meaningful name.
This method computes the max series of a same character. So, you could call it computeMaxSeries()
3) And instead being a void method, you could return the max series number.
4) Besides this :
for (int a = 0; a < adriana.length(); a++) {
if (adriana.charAt(a) == adriana.charAt(a + 1)) {
will throw a StringIndexOutOfBoundsException as adriana.charAt(a + 1) refers to an index beyond the valid limit of the String length.
You should rather iterate until the last index -1 :
for (int a = 0; a < adriana.length()-1; a++) {
5) At last this is not consistent since you update maxreps by relying on maxreps instead of current :
if(maxreps>=current){
maxreps=current;
}
You should rather write :
if (current >= maxreps) {
maxreps = current;
}
So, finally the method would be :
public int computeMaxSeries(){
int current=1;
int maxreps=1;
String adriana = "aabbddddnsspkrrgg";
for(int a=0; a<adriana.length()-1; a++){
if(adriana.charAt(a) == adriana.charAt(a+1)){
current++;
if (current >= maxreps) {
maxreps = current;
}
}
}
return maxreps;
}
Now you can do :
final int maxreps = fritz.computeMaxSeries();
System.out.println(maxreps);
Doing a java project for CS class that entails us making a dec to binary converter with 2 classes (one being the tester). The teacher insists we don't contact him for help. Not really sure what I can do on this because it tells me "error: cannot find symbol" and points at the pn.charAt in the latter half of the code. Any help or hints would be much appreciated.
Converter
public class BinaryNumber {
private String n;
public BinaryNumber(String pn) {
n = pn;
}
public String getN() {
return n;
}
public int convertToDecimal() {
int bitPosition = 0;
int sum = 0;
for (int i = n.length() - 1; i >= 0; i--) {
sum = sum + (int) Math.pow(2, bitPosition) * (pn.charAt + (i) - 48);
//System.out.println(n.charAt (i));
}
return sum;
}
public int add(BinaryNumber obn) {
return convertToDecimal() + obn.convertToDecimal();
}
public int sub(BinaryNumber obn) {
return convertToDecimal() - obn.convertToDecimal();
}
}
Test Class
public class BinaryNumberTest {
public static void main(String[] args) {
BinaryNumber bn = new BinaryNumber("1011");
BinaryNumber bn1 = new BinaryNumber("1111");
System.out.println(bn.convertToDecimal());
System.out.println(bn.add(b1));
}
}
Your pn is defined as a parameter in your constructor BinaryNumber() so it has "local scope", it doesn't exist outside of the function.
What you should be using in convertToDecimal() would be your global variable n instead.
And if pn or n are Strings, then your usage of charAt is also incorrect since it is suppose to be a function. If I had to extrapolate, I think you're trying to use i as your charAt() positioning?
The changes to fix these two errors would look like this:
sum = sum + (int) Math.pow(2, bitPosition) * (n.charAt(i) - 48);
I want to convert String input into int using recursion. This is the code I came up with but if my input is 123456 it only returns 124. If I enter 1234567, it gives an error.
import java.util.*;
public class Problem1 {
static int x =0;
static int counter = 0;
//input
public static void main(String[] args) {
Scanner scan = new Scanner (System.in);
String s= scan.nextLine();
System.out.println(recursive(s));
}
//recursive method
public static int recursive(String s){
if(s.length()==1){
x=(x*10)+ Integer.parseInt(s.substring(0,1));
return x;
}
else{
x = (x*10)+Integer.parseInt(s.substring(0,1));
counter++;
return recursive(s.substring(counter,s.length()-1));
}
}
}
import java.util.Scanner;
public class Problem1 {
static int x = 0;
static int counter = 0;
// input
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
String s = scan.nextLine();
System.out.println(recursive(s));
}
// recursive method
public static int recursive(String s) {
if (s.length() == 1) {
x = (x * 10) + Integer.parseInt(s.substring(0, 1));
return x;
} else {
x = (x * 10) + Integer.parseInt(s.substring(0, 1));
counter++;
return recursive(s.substring(1, s.length()));
}
}
}
Look at your static counter variable. You are incrementing it every time. But you only want to have the substring starting at 1 (so cut off the first "letter").
So instead of using:
counter++;
return recursive(s.substring(counter,s.length()-1));
consider using:
return recursive(s.substring(1)); // you even don't really need the length
Because the String s parameter is as follows:
1st call: 1234567
2nd call: 234567
3rd call: 34567
4th call: 4567
...
So, you only have to cut off the first letter.
Btw: your sample "project" is a really funny one ;)
A few notes to start:
If you're doing recursion, you probably don't want to use a member variable. It's not wrong to do so, but not really typical of the pattern (your x variable).
It's often handy to pass in state through the recursion, although you wouldn't have to (that is, current value of x).
Your case is a little odd because you have to change your current parse value for every sub-parse (shifting by 10 each time); makes it a little more complicated.
If you are going to keep x as a member variable (which does seem to make sense in this case), you don't need to return anything from recursive.
Can you really not just use Integer.parseInt()?
Code could be much more simple, something like:
void recursive (String s)
{
if (s.length() == 0) return 0;
x = x * 10 + Integer.parseInt(s.substring(0, 1));
recursive(s.substring(1));
}
recursion("1234567", 0, 1)
The above code will turn the string "1234567" into an int using recursion. You must pass the string you want to convert, and then 0 and 1.
public static int recursion(String s, int result, int place) {
result += place * Integer.parseInt(s.charAt(s.length() - 1) + "");
if(s.length() == 1) {
return result;
}
else {
return recursion(s.substring(0, s.length() - 1), result, place * 10);
}
}
public static int computeStr(String str) {
if (str.equals("")) {
return 0;
}
int x = 1;
for (int i = 0; i < str.length() - 1; i++) {
x = x * 10;
}
x = x * Integer.parseInt(str.substring(0, 1));
return x + computeStr(str.substring(1));
}
For example: "2432" is (2 * 1000) + (4 * 100) + (3*10) + (2*1) = 2432
this algorithm begins at first position (2) from 2432
I know its kind of a late response but you could try something like this :-
private static int stringToInt(String string) {
if (string.length() == 0) {
return 0;
}
int rv;
int num = string.charAt(string.length() - 1) - '0';
String restOfTheString = string.substring(0, string.length() - 1);
rv = stringToInt(restOfTheString) * 10 + num;
return rv;
}
Try something like this:
Subtracting the ASCII code of the '0' character from your character returns an integer:
public class StringRecursion {
static int counter = 0;
public static void main(String[] args) {
System.out.println(convertStringToInt("123456"));
}
public static int convertStringToInt(String input) {
if (input.length() == 1)
return input.charAt(0) - '0';
int value = convertStringToInt(input.substring(0, input.length() - 1));
counter++;
return value * 10 + input.charAt(counter) - '0';
}
}
Try it like this :
public static int conStrToInt(String str) {
if(str.length()==0)
{
return 0;
}
char cc = str.charAt(0);
String ros = str.substring(1);
int factor=1;
for(int i=0;i<str.length()-1;i++)
factor*=10;
factor=factor*(cc-'0');
return factor+conStrToInt(ros);
}
I'm having an extremely difficult time getting a private method with arguments to be usable in my toString method but have no idea how to get the two methods to cooperate.
main class:
import static java.lang.System.*;
public class Triples
{
private int number;
public Triples()
{
//this(0);
}
public Triples(int num)
{
number = num;
}
public void setNum(int num)
{
number = num;
}
private int greatestCommonFactor(int a, int b, int c)
{
int max = number;
for(int n = 1; n <= max; n++)
{
for(a = n; a <= max; a++)
{
a = n;
for(b = a +1; b <= max; b++)
{
b =n;
for(c = b + 1; c <= max; c++)
{
c = n;
if(Math.pow(a, 2)+ Math.pow(b, 2)== Math.pow(c, 2))
{
if((a%2==1 && b%2==0)|| (a%2==0 && b%2==1))
{
if(a%2<=1 && b%2<=1 && c%2<=1)
{
String last = a + "" + b + c;
}
}
}
}
}
}
}
return 1;
}
public String toString()
{
String output="";
output = output + this.greatestCommonFactor( ) + " \n";
return output;
}
}
and for cross-referencing my runner class:
import static java.lang.System.*;
import java.util.Scanner;
public class Lab11j
{
public static void main(String args[])
{
Scanner keyboard = new Scanner(System.in);
String choice="";
do{
out.print("Enter the max number to use : ");
int big = keyboard.nextInt();
//instantiate a TriangleThree object
Triples triple = new Triples(big);
//call the toString method to print the triangle
out.println( triple );
System.out.print("Do you want to enter more data? ");
choice=keyboard.next();
}while(choice.equals("Y")||choice.equals("y"));
}
}
if you find you need clarification of this lab, here's a Google docs of the labsheet: https://docs.google.com/open?id=0B_ifaCiEZgtcX08tbW1jNThZZmM
The variables a, b & c can be used as local variables here. This would allow you to remove them from the argument list of greatestCommonFactor:
private int greatestCommonFactor() {
int a = 0;
int b = 0;
int c = 0;
...
as they are only required within the scope of the method.
Well, yeah. You're not passing anything to greatestCommonFactor. I'm not sure what you expected to happen in your toString() method when you didn't pass enough arguments to a method.
you need to pass them like
output = output + this.greatestCommonFactor(1,2,3) + " \n";
the thing is, unless you are passing parameters to toString, without this, this code seems very limited. Alternatively you need to set some fields on the class with what will be passed into your function.
I cant get how to use/create oop code without word static. I read Sun tutorials, have book and examples. I know there are constructors, then "pointer" this etc. I can create some easy non-static methods with return statement. The real problem is, I just don't understand how it works.I hope some communication gives me kick to move on. If someone asks, this is not homework. I just want to learn how to code.
The following code are static methods and some very basic algorithms. I'd like to know how to change it to non-static code with logical steps(please.)
The second code shows some non-static code I can write but not fully understand nor use it as template to rewrite the first code.
Thanks in advance for any hints.
import java.util.Scanner;
/**
*
* #author
*/
public class NumberArray2{
public static int[] table() {
Scanner Scan = new Scanner(System.in);
System.out.println("How many numbers?");
int s = Scan.nextInt();
int[] tab = new int[s];
System.out.println("Write a numbers: ");
for(int i=0; i<tab.length; i++){
tab[i] = Scan.nextInt();
}
System.out.println("");
return tab;
}
static public void output(int [] tab){
for(int i=0; i<tab.length; i++){
if(tab[i] != 0)
System.out.println(tab[i]);
}
}
static public void max(int [] tab){
int maxNum = 0;
for(int i=0; i<tab.length; i++){
if(tab[i] > maxNum)
maxNum = tab[i];
}
//return maxNum;
System.out.println(maxNum);
}
static public void divide(int [] tab){
for(int i=0; i<tab.length; i++){
if((tab[i] % 3 == 0) && tab[i] != 0)
System.out.println(tab[i]);
}
}
static public void average(int [] tab){
int sum = 0;
for(int i=0; i<tab.length; i++)
sum = sum + tab[i];
int avervalue = sum/tab.length;
System.out.println(avervalue);
}
public static void isPrime(int[] tab) {
for (int i = 0; i < tab.length; i++) {
if (isPrimeNum(tab[i])) {
System.out.println(tab[i]);
}
}
}
public static boolean isPrimeNum(int n) {
boolean prime = true;
for (long i = 3; i <= Math.sqrt(n); i += 2) {
if (n % i == 0) {
prime = false;
break;
}
}
if ((n % 2 != 0 && prime && n > 2) || n == 2) {
return true;
} else {
return false;
}
}
public static void main(String[] args) {
int[] inputTable = table();
//int s = table();
System.out.println("Written numbers:");
output(inputTable);
System.out.println("Largest number: ");
max(inputTable);
System.out.println("All numbers that can be divided by three: ");
divide(inputTable);
System.out.println("Average value: ");
average(inputTable);
System.out.println("Prime numbers: ");
isPrime(inputTable);
}
}
Second code
public class Complex {
// datové složky
public double re;
public double im;
// konstruktory
public Complex() {
}
public Complex(double r) {
this(r, 0.0);
}
public Complex(double r, double i) {
re = r;
im = i;
}
public double abs() {
return Math.sqrt(re * re + im * im);
}
public Complex plus(Complex c) {
return new Complex(re + c.re, im + c.im);
}
public Complex minus(Complex c) {
return new Complex(re - c.re, im - c.im);
}
public String toString() {
return "[" + re + ", " + im + "]";
}
}
Let's start with a simple example:
public class Main
{
public static void main(final String[] argv)
{
final Person personA;
final Person personB;
personA = new Person("John", "Doe");
personB = new Person("Jane", "Doe");
System.out.println(personA.getFullName());
System.out.println(personB.getFullName());
}
}
class Person
{
private final String firstName;
private final String lastName;
public Person(final String fName,
final String lName)
{
firstName = fName;
lastName = lName;
}
public String getFullName()
{
return (lastName + ", " + firstName);
}
}
I am going to make a minor change to the getFullName method now:
public String getFullName()
{
return (this.lastName + ", " + this.firstName);
}
Notice the "this." that I now use.
The question is where did "this" come from? It is not declared as a variable anywhere - so it is like magic. It turns out that "this" is a hidden parameter to each instance method (an instance method is a method that is not static). You can essentially think that the compiler takes your code and re-writes it like this (in reality this is not what happens - but I wanted the code to compile):
public class Main
{
public static void main(final String[] argv)
{
final Person personA;
final Person personB;
personA = new Person("John", "Doe");
personB = new Person("Jane", "Doe");
System.out.println(Person.getFullName(personA));
System.out.println(Person.getFullName(personB));
}
}
class Person
{
private final String firstName;
private final String lastName;
public Person(final String fName,
final String lName)
{
firstName = fName;
lastName = lName;
}
public static String getFullName(final Person thisx)
{
return (thisx.lastName + ", " + thisx.firstName);
}
}
So when you are looking at the code remember that instance methods have a hidden parameter that tells it which actual object the variables belong to.
Hopefully this gets you going in the right direction, if so have a stab at re-writing the first class using objects - if you get stuck post what you tried, if you get all the way done post it and I am sure we help you see if you got it right.
First, OOP is based around objects. They should represent (abstract) real-world objects/concepts. The common example being:
Car
properties - engine, gearbox, chasis
methods - ignite, run, brake
The ignite method depends on the engine field.
Static methods are those that do not depend on object state. I.e. they are not associated with the notion of objects. Single-program algorithms, mathematical calculations, and such are preferably static. Why? Because they take an input and produce output, without the need to represent anything in the process, as objects. Furthermore, this saves unnecessary object instantiations.
Take a look at java.lang.Math - it's methods are static for that precise reason.
The program below has been coded by making the methods non-static.
import java.util.Scanner;
public class NumberArray2{
private int tab[]; // Now table becomes an instance variable.
// allocation and initilization of the table now happens in the constructor.
public NumberArray2() {
Scanner Scan = new Scanner(System.in);
System.out.println("How many numbers?");
int s = Scan.nextInt();
tab = new int[s];
System.out.println("Write a numbers: ");
for(int i=0; i<tab.length; i++){
tab[i] = Scan.nextInt();
}
System.out.println("");
}
public void output(){
for(int i=0; i<tab.length; i++){
if(tab[i] != 0)
System.out.println(tab[i]);
}
}
public void max(){
int maxNum = 0;
for(int i=0; i<tab.length; i++){
if(tab[i] > maxNum)
maxNum = tab[i];
}
System.out.println(maxNum);
}
public void divide(){
for(int i=0; i<tab.length; i++){
if((tab[i] % 3 == 0) && tab[i] != 0)
System.out.println(tab[i]);
}
}
public void average(){
int sum = 0;
for(int i=0; i<tab.length; i++)
sum = sum + tab[i];
int avervalue = sum/tab.length;
System.out.println(avervalue);
}
public void isPrime() {
for (int i = 0; i < tab.length; i++) {
if (isPrimeNum(tab[i])) {
System.out.println(tab[i]);
}
}
}
public boolean isPrimeNum(int n) {
boolean prime = true;
for (long i = 3; i <= Math.sqrt(n); i += 2) {
if (n % i == 0) {
prime = false;
break;
}
}
if ((n % 2 != 0 && prime && n > 2) || n == 2) {
return true;
} else {
return false;
}
}
public static void main(String[] args) {
// instatiate the class.
NumberArray2 obj = new NumberArray2();
System.out.println("Written numbers:");
obj.output(); // call the methods on the object..no need to pass table anymore.
System.out.println("Largest number: ");
obj.max();
System.out.println("All numbers that can be divided by three: ");
obj.divide();
System.out.println("Average value: ");
obj.average();
System.out.println("Prime numbers: ");
obj.isPrime();
}
}
Changes made:
int tab[] has now been made an
instance variable.
allocation and initialization of the
table happens in the constructor.
Since this must happen for every
instantiated object, it is better to
keep this in a constructor.
The methods need not be called with
table as an argument as all methods
have full access to the instance
variable(table in this case)
The methods have now been made
non-static, so they cannot be called
using the class name, instead we need
to instantiate the class to create an
object and then call the methods on
that object using the obj.method()
syntax.
It is easy to transform class methods from beeing static to non-static. All you have to do is remove "static" from all method names. (Ofc dont do it in public static void main as you would be unable to run the example)
Example:
public static boolean isPrimeNum(int n) { would become
public boolean isPrimeNum(int n) {
In public static void main where you call the methods you would have to chang your calls from beeing static, to refere to an object of the specified class.
Before:
NumberArray2.isPrimeNum(11);
After:
NumberArray2 numberarray2 = new NumberArray2(); // Create object of given class
numberarray2.isPrimeNum(11); // Call a method of the given object
In NumberArray2 you havent included an constructor (the constructor is like a contractor. He takes the blueprint (class file, NumberArray2) and follows the guidelines to make for example a building (object).
When you deside to not include a constructor the java compilator will add on for you. It would look like this:
public NumberArray2(){};
Hope this helps. And you are right, this looks like homework :D
I belive its common practice to supply the public modifier first. You haven done this in "your" first method, but in the others you have static public. Atleast for readability you should do both (code will compile ether way, as the compilator dosnt care).
The code is clean and easy to read. This is hard to do for someone who is "just want to learn how to code". Hope this helps you on your way with your "justlookslikehomeworkbutisnt" learning.
I'm guessing you're confused of what "static" does. In OOP everything is an object. Every object has its own functions/variables. e.g.
Person john = new Person("John",18);
Person alice = new Person("Alice",17);
if the function to set the 'name' variable would be non static i.e. string setName(string name){} this means that the object john has a name "John" and the object alice has a name "Alice"
static is used when you want to retain a value of something across all objects of the same class.
class Person{
static int amountOfPeopleCreated;
public Person(string name, int age){
amountOfPeopleCreated++;
setName(name);
setAge(age);
}
...
}
so if you'd the value of amountOfPeopleCreated will be the same no matter if you check alice or john.