Develop Reference

How can i shorten this code and make it less repetitive?

I made a simple calculator but the if statements are very repetitive and long. I am wondering what other solution I could use to shorten it and make it less repetitive. For example using a method (which i have tried but not succeeded) or any other techniques that are usable. Preferably not too advanced since I'm a beginner.
import static java.lang.System.*;
import static javax.swing.JOptionPane.*;
import static java.lang.Integer.*;
public class SimpleCalc {
public static void main(String[] args) {
String operator = showInputDialog("Choose operation: " + "\n" +
"[1] = Plus" + "\n" +
"[2] = Minus" + "\n" +
"[3] = Multiply" + "\n" +
"[4] = Divide" + "\n");
int c = parseInt(operator);
if (c > 4) {
showMessageDialog(null, "You cant do that.");
} else if (c == 1) {
String textA = showInputDialog("Enter first number: ");
String textB = showInputDialog("Enter second number: ");
int a = parseInt(textA);
int b = parseInt(textB);
showMessageDialog(null, a + " + " + b + " = " + (a + b));
} else if (c == 2) {
String textA = showInputDialog("Enter first number: ");
String textB = showInputDialog("Enter second number: ");
int a = parseInt(textA);
int b = parseInt(textB);
showMessageDialog(null, a + " - " + b + " = " + (a - b));
} else if (c == 3) {
String textA = showInputDialog("Enter first number: ");
String textB = showInputDialog("Enter second number: ");
int a = parseInt(textA);
int b = parseInt(textB);
showMessageDialog(null, a + " * " + b + " = " + (a * b));
} else if (c == 4) {
String textA = showInputDialog("Enter first number: ");
String textB = showInputDialog("Enter second number: ");
int a = parseInt(textA);
int b = parseInt(textB);
showMessageDialog(null, a + " / " + b + " = " + (a / b));
}
}
}

Try something like
String textA = showInputDialog("Enter first number: ");
String textB = showInputDialog("Enter second number: ");
int a = parseInt(textA);
int b = parseInt(textB);
switch(c) {
case 1:
showMessageDialog(null, a + " + " + b + " = " + (a+b));
break;
case 2:
...
default:
showMessageDialog(null, "You cant do that.");

Well, to start; you can move the
String textA = showInputDialog("Enter first number: ");
String textB = showInputDialog("Enter second number: ");
int a = parseInt(textA);
int b = parseInt(textB);
outside of the if blocks so that it only asks once before the if block, which will save you 12 lines of code.
Or you can also use methods or functions as a practice; but that wouldn't shorten your code further, really. I'd also suggest looking into Codegolf, you can learn a LOT about code-shortening.

The following will be identical, but doesn't repeat the same lines over and over. You can also use the switch statement in place of the 4 if/else if statements.
public class SimpleCalc {
public static void main(String[] args) {
String operator = showInputDialog("Choose operation: " + "\n" +
"[1] = Plus" + "\n" +
"[2] = Minus" + "\n" +
"[3] = Multiply" + "\n" +
"[4] = Divide" + "\n");
int c = parseInt(operator);
if (c>4) {
showMessageDialog(null, "You cant do that.");
return;
}
String textA = showInputDialog("Enter first number: ");
String textB = showInputDialog("Enter second number: ");
int a = parseInt(textA);
int b = parseInt(textB);
if(c==1) {
showMessageDialog(null, a + " + " + b + " = " + (a+b));
}
else if (c==2) {
showMessageDialog(null, a + " - " + b + " = " + (a-b));
}
else if (c==3) {
showMessageDialog(null, a + " * " + b + " = " + (a*b));
}
else if (c==4) {
showMessageDialog(null, a + " / " + b + " = " + (a/b));
}
}
}

There are a couple approaches:
Put the common code into a method
Move the common code to a different part of the current method so that it is executed unconditionally.
Put the non-common code into a function / method / class that can be used to parameterize the common code.
In this case, the second approach works best; e.g.
if(c==1) {
String textA = showInputDialog("Enter first number: ");
String textB = showInputDialog("Enter second number: ");
int a = parseInt(textA);
int b = parseInt(textB);
showMessageDialog(null, a + " + " + b + " = " + (a+b));
}
else if (c==2) {
String textA = showInputDialog("Enter first number: ");
String textB = showInputDialog("Enter second number: ");
int a = parseInt(textA);
int b = parseInt(textB);
showMessageDialog(null, a + " - " + b + " = " + (a-b));
}
...
can be transformed into:
String textA = showInputDialog("Enter first number: ");
String textB = showInputDialog("Enter second number: ");
int a = parseInt(textA);
int b = parseInt(textB);
int result;
char op;
if (c == 1) {
result = a + b;
op = '+';
} else if (c == 2) {
result = a - b;
op = '-';
}
...
showMessageDialog(null, a + " " + op + " " + b + " = " + result);
(I have left a problem there for you to notice and sort out ... as a learning exercise.)

Just for fun. Factor out the stuff that's common! And handle the possibility that you'll need to implement unary operators. You'll probably also want to put it in a loop, and add an exit command.
public class SimpleCalc {
public static void main(String[] args) {
String operator = showInputDialog(
"Choose operation: " + "\n" +
"[1] = Add" + "\n" +
"[2] = Subtract" + "\n" +
"[3] = Multiply" + "\n" +
"[4] = Divide" + "\n");
"[5] = Negate" + "\n");
int c = parseInt(operator);
int operand_count = 0;
switch (c) {
case 1:
case 2:
case 3:
case 4:
operand_count = 2;
break;
case 5:
operand_count = 1;
break;
default:
showMessageDialog(null, "You cant do that.");
return(-1);
}
int a = 0;
int b = 0;
if (operand_count >= 1) {
String textA = showInputDialog("Enter first number: ");
int a = parseInt(textA);
}
if (operand_count >= 2) {
String textB = showInputDialog("Enter second number: ");
int b = parseInt(textB);
}
char * opname = "";
int result = 0;
switch (c) {
case 1:
opname = "+";
result = a + b;
break;
case 2:
opname = "-";
result = a - b;
break;
case 3:
opname = "*";
result = a * b;
break;
case 4:
opname = "/";
result = a / b;
break;
case 5:
opname = "-";
result = -a;
break;
}
if (operand_count == 1) {
showMessageDialog(null, opname + " (" + a + ") = " result);
} else {
showMessageDialog(null, a + " " + opname + " " + b + " = " + result);
}
}
}

(Java) Swapping variables, which method is quickest and uses the least memory?

Suppose I wanna swap variables with eachother. Which of the solutions below would be the faster and requires less memory? Note: there is only 2 variables to be swapped here, but imagined we had one billion variables to be swapped.
Solution 1:
public class Exc15 {
public static void main(String[] args) {
int c = 1;
int d = 2;
int e = c;
System.out.println(c + " " + d);
c = d;
d = e;
System.out.println(c + " " + d);
}
}
Solution 2:
public class test {
public static void main(String[] args) {
int a = 3;
int b = 4;
System.out.println(a + " " + b);
a = a + b;
b = a - b;
a = a - b;
System.out.println(a + " " + b);
}
}

Output copied twice in Nim game in Java

Im learning java with "programmingbydoing" and i have a problem with Nim game, everything works fine apart from one thing, which is that both:
"System.out.print(n1 + ", choose a pile: ");"
and
"System.out.print(n2 + ", choose a pile: ");"
is out printed twice after the first time.
Here is code:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Player one, enter your name: ");
String n1 = input.nextLine();
System.out.print("Player two, enter your name: ");
String n2 = input.nextLine();
int a = 3;
int b = 4;
int c = 5;
int count = 1;
System.out.println("A: "+a+" B: "+b+" C: "+c);
nim_loop:while(a > 0 || b > 0 || c > 0) {
while(count % 2 != 0 ) {
System.out.print(n1+", choose a pile: ");
String first = input.nextLine();
if (first.contains("a") || first.contains("A")) {
System.out.print("How many to remove from pile " + first + "? ");
int second = input.nextInt();
count = count + 1;
a = a - second;
System.out.println("A: " + a + " B: " + b + " C: " + c);
if(a <= 0 && b <= 0 && c <= 0){
break nim_loop;
}
}
else if (first.contains("b") || first.contains("B")) {
System.out.print("How many to remove from pile " + first + "? ");
int second = input.nextInt();
count = count + 1;
b = b - second;
System.out.println("A: " + a + " B: " + b + " C: " + c);
if(a <= 0 && b <= 0 && c <= 0){
break nim_loop;
}
}
else if (first.contains("c") || first.contains("C")) {
System.out.print("How many to remove from pile " + first + "? ");
int second = input.nextInt();
count = count + 1;
c = c - second;
System.out.println("A: " + a + " B: " + b + " C: " + c);
if(a <= 0 && b <= 0 && c <= 0){
break nim_loop;
}
}
}
while(count % 2 == 0) {
System.out.print(n2 + ", choose a pile: ");
String third = input.nextLine();
if (third.contains("a") || third.contains("A")) {
System.out.print("How many to remove from pile " + third + "? ");
int fourth = input.nextInt();
count = count + 1;
a = a - fourth;
System.out.println("A: " + a + " B: " + b + " C: " + c);
} else if (third.contains("b") || third.contains("B")) {
System.out.print("How many to remove from pile " + third + "? ");
int fourth = input.nextInt();
count = count + 1;
b = b - fourth;
System.out.println("A: " + a + " B: " + b + " C: " + c);
} else if (third.contains("c") || third.contains("C")) {
System.out.print("How many to remove from pile " + third + "? ");
int fourth = input.nextInt();
count = count + 1;
c = c - fourth;
System.out.println("A: " + a + " B: " + b + " C: " + c);
}
}
}
if (count % 2 != 0) {
System.out.println("Game ended, Player " + n1 + " is a winner.");
} else if (count % 2 == 0){
System.out.println("Game ended, Player " + n2 + " is a winner.");
}
}
}
And here are the pictures of what happens when i run it:

When the first if condition in first inner loop is true and when you get the user input by using nextInt() it only reads the int value and does not consume the last new line character i,e \n. So the subsequent call to nextLine() will be skipped i,e the nextLine() call in second inner while loop will be skipped without any value but System.out.print(n2 + ", choose a pile: "); will be printed as it is before nextLine() call and control goes back to outer while loop.
Now the count value is 2 so first inner while condition will be false and control goes to second inner while loop. And again it prints b, choose a pile:. Hope this clears your question
Workaround is fire a blank nextLine() call after every nextInt() or use nextLine() inside if condition and parse the user input using Integer.parseInt(String) method.
Example code :
if (first.contains("a") || first.contains("A")) {
System.out.print("How many to remove from pile " + first + "? ");
int second = input.nextInt();
input.nextLine(); // firing an blank nextLine call
count = count + 1;
a = a - second;
System.out.println("A: " + a + " B: " + b + " C: " + c);
if(a <= 0 && b <= 0 && c <= 0){
break nim_loop;
}
For more information - Scanner is skipping nextLine() after using next(), nextInt() or other nextFoo() methods

Printing a string?

I'm in my first programming class; can anyone help me understand why I can't print my last line please?
package program4;
import java.util.*;
public class Program4 {
public static void main(String[] args) {
int a, b, c, numComparisons;
String comparisons = "Comparisons for triangleType determination: ";
Scanner scan = new Scanner(System.in);
for (int i = 0; i < 7; i++) {
}
String triangleType = "";
System.out.print("Enter 3 positive integer lengths for the sides of a "
+ "triangle:");
a = scan.nextInt();
b = scan.nextInt();
c = scan.nextInt();
System.out.println("The input lengths are: a = " + a + ", b = " + b + ", and"
+ " c = " + c + "");
if ((a + b < c) || (b + c < a) || (a + c < b)) {
System.out.print("There is no triangle with sides " + a + ", " + b + " and "
+ "" + c + ".");
} else {
numComparisons = 1;
comparisons += "a==b";
if (a == b) {
comparisons += "(T)" + "(b==c)";
numComparisons++;
if (b == c) {
comparisons += "(T)";
triangleType = "Equilateral";
}
} else {
comparisons += "(F)";
if (a == c) {
comparisons += "(T)";
triangleType = "Isosceles";
} else {
comparisons += "b==c";
numComparisons++;
comparisons += "(F)";
if (b == c) {
triangleType = "Isosceles";
} else {
comparisons += "a==c";
numComparisons++;
comparisons += "(F)";
triangleType = "Scalene";
}
}
}
System.out.printf("" + comparisons + (""));
System.out.printf("numComparisons = " + numComparisons);
System.out.println("The triangles with sides " + a + ", "
+ " + b + ", and " + c + ", is + triangleType + ");
}
}
}

Your last line syntax is pretty messed up.
this
System.out.println("The triangles with sides " + a + ", "
+ " + b + ", and " + c + ", is + triangleType + ");
should be
System.out.println("The triangles with sides " + a + ", "
+ b + ", and " + c + ", is " + triangleType);

System.out.println("The triangles with sides " + a + ", "
+ " + b + ", and " + c + ", is + triangleType + ");
What IDE/editor are you using? It should should show you the errors here. This should be
System.out.println("The triangles with sides " + a + ", "
+ b + ", and " + c + ", is" + triangleType);
This is better

Solving quadratic equation USING METHODS, java

I have a java program written for solving the quadratic equation but the assignment requires me to have methods for each of the tasks: displaying the equation, determining if the equation has real solutions, calculating a solution, and displaying the solutions if they exist. I have methods for everything except for checking if the solutions are real except my methods are saying that they are undefined. Can someone please help me format my methods, I don't quite know how to implement them? here is the code I have thus far:
import java.util.Scanner;
public class QuadraticFormula {
public static void main(String[] args)
{
//Creating scanner and variables
Scanner s = new Scanner(System.in);
System.out.println("Insert value for a: ");
double a = Double.parseDouble(s.nextLine());
System.out.println("Insert value for b: ");
double b = Double.parseDouble(s.nextLine());
System.out.println("Insert value for c: ");
double c = Double.parseDouble(s.nextLine());
//Display format for negatives
displayEquation(double a, double b, double c);{
if (b > 0 && c > 0 ){
System.out.println(a + "x^2 + " + b + "x + " + c + " =0");}
if (b < 0 && c > 0 ){
System.out.println(a + "x^2 " + b + "x + " + c + " =0");}
if (b > 0 && c < 0 ){
System.out.println(a + "x^2 + " + b + "x " + c + " =0");}
if (b < 0 && c < 0 ){
System.out.println(a + "x^2 " + b + "x " + c + " =0");}
s.close();
}
//The work/formula
private static double calculateSolution(double a, double b, double c);
{
double answer1 = (-b + Math.sqrt(Math.pow(b, 2) - (4 * a * c))) / (2 * a);
return answer1;
}
private static double calculateSolution(double a, double b, double c);
{
double answer2 = (-b - Math.sqrt(Math.pow(b, 2) - (4 * a * c))) / (2 * a);
return answer2;
}
//Display results and check if the solution is imaginary (real or not)
private static void displaySolutions(double answer1, double answer2); {
if (Double.isNaN(answer1) || Double.isNaN(answer2))
{
System.out.println("Answer contains imaginary numbers");
} else System.out.println("The values are: " + answer1 + ", " + answer2);
}
}
}

Your methods need to be defined outside your main method. You can then call them in your main method like this:
displayEquation(a, b, c);
You also should remove the semicolons after your method definitions. It should look like this:
public class QuadraticFormula {
public static void main(String[] args)
{
//Creating scanner and variables
Scanner s = new Scanner(System.in);
System.out.println("Insert value for a: ");
double a = Double.parseDouble(s.nextLine());
System.out.println("Insert value for b: ");
double b = Double.parseDouble(s.nextLine());
System.out.println("Insert value for c: ");
double c = Double.parseDouble(s.nextLine());
s.close();
}
//Display format for negatives
public static void displayEquation(double a, double b, double c) {
if (b > 0 && c > 0 ){
System.out.println(a + "x^2 + " + b + "x + " + c + " =0");}
if (b < 0 && c > 0 ){
System.out.println(a + "x^2 " + b + "x + " + c + " =0");}
if (b > 0 && c < 0 ){
System.out.println(a + "x^2 + " + b + "x " + c + " =0");}
if (b < 0 && c < 0 ){
System.out.println(a + "x^2 " + b + "x " + c + " =0");}
}
private static double calculateSolution(double a, double b, double c) {
double answer2 = (-b - Math.sqrt(Math.pow(b, 2) - (4 * a * c))) / (2 * a);
return answer2;
}
//Display results and check if the solution is imaginary (real or not)
private static void displaySolutions(double answer1, double answer2) {
if (Double.isNaN(answer1) || Double.isNaN(answer2))
{
System.out.println("Answer contains imaginary numbers");
}
else System.out.println("The values are: " + answer1 + ", " + answer2);
}
}