Develop Reference

Menu loop in 2 different methods Java program

I am working on a menu program and I want to be able to enter as many selections as I want without the menu looping as well after the input, currently it either infinite-loops, or the program ends after one input, being unable to perform a different selection after the first. Also I want to have a case where I exit the menu if I press 0.
public void showMenu() {
System.out.println("Welcome!");
System.out.println("Select an option:\n" +
"1. Adunare\n" +
"2. Scadere\n" +
"3. Inmultire\n" +
"4. Impartire\n" +
"5. Comparare numere\n" +
"6. List To Hundred\n" +
"7. Nr to list\n" +
"8. Contains\n" +
"9. Even numbers\n" +
"10. List of Strings\n" +
"11. Second largest number\n" +
"12. Second lowest number\n" +
"13. Number \n" +
"14. Number 2 \n" +
"15. Number 3\n" +
"16. String\n" +
"17. String 2\n" +
"18. Amount of snow\n" +
"19. Eligible to vote test\n" +
"20. Odd or even\n" +
"21. Dog\n" +
"22. Cat\n" +
"23. Elev");
}
public void runProgram() {
showMenu();
int numberFromUser = citire.readNumbers();
do {
switch (numberFromUser) {
case 1:
addition();
break;
case 2:
subtraction();
break;
case 3:
multiply();
break;
case 4:
divide();
break;
case 5:
comparareNumere();
break;
case 6:
listhundred();
break;
case 7:
setnumbertolist();
break;
case 8:
contain();
break;
case 9:
limit();
break;
case 10:
list();
break;
case 11:
secmax();
break;
case 12:
secmin();
break;
case 13:
nr();
break;
case 14:
nr2();
break;
case 15:
nr3();
break;
case 16:
string();
break;
case 17:
string2();
break;
case 18:
weather();
break;
case 19:
eligible();
break;
case 20:
oddoreven();
break;
case 21:
dog();
break;
case 22:
cat();
break;
case 23:
elev();
break;
default:
break;
}
} while (numberFromUser != 0);
}

Add
numberFromUser = citire.readNumbers();
into the loop to take numbers in the loop.
public void runProgram() {
showMenu();
int numberFromUser;
do {
numberFromUser = citire.readNumbers();
switch (numberFromUser) {
case 1:
addition();
break;
case 2:
subtraction();
break;
case 3:
multiply();
break;
case 4:
divide();
break;
case 5:
comparareNumere();
break;
case 6:
listhundred();
break;
case 7:
setnumbertolist();
break;
case 8:
contain();
break;
case 9:
limit();
break;
case 10:
list();
break;
case 11:
secmax();
break;
case 12:
secmin();
break;
case 13:
nr();
break;
case 14:
nr2();
break;
case 15:
nr3();
break;
case 16:
string();
break;
case 17:
string2();
break;
case 18:
weather();
break;
case 19:
eligible();
break;
case 20:
oddoreven();
break;
case 21:
dog();
break;
case 22:
cat();
break;
case 23:
elev();
break;
default:
break;
}
} while (numberFromUser != 0);
}

Try changing runProgram to following :
public void runProgram()
{
int numberFromUser;
showMenu();
while(true)
{
System.out.print("Enter choice: ");
numberFromUser = citire.readNumbers();
switch(NumberFromUser)
{
// All your case statements
case 0: System.exit(0);
}
}
}

Keep getting Null on String with Random

it's Java Starter here, so i was Coding my program which makes a Password, i used the Random Object to have a random Number that will choose what Letter comes or What number comes.
I keep getting the Numbers and the Symbols Only.. what i get is something Like this:
"9=9null=99" I don't understand Why there's a null. Java doesn't show me any problems with my code (Doesn't show Null Pointer exception.)
Here's My code:
package project.Secureword.com;
import java.awt.*;
import java.awt.event.*;
import java.util.Objects;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
import java.util.Random;
import javax.swing.*;
public class Main {
private static JFrame start;
private static TextField field;
private static String password;
private static String lastpass;
public static Settings passsettings;
public static Random r;
public static void main(String[] args) {
passsettings = new Settings();
passsettings.setIfDots(true);
passsettings.setIfLowercase(true);
passsettings.setIfNum(true);
passsettings.setIfUpprcase(true);
Settings.changerun();
start();
}
public static void start() {
Font a = new Font(null, Font.BOLD, 0);
Font size = a.deriveFont(20f);
JButton createPass = new JButton();
createPass.setText("<html> Click me to <br> Generate a Password! <html>");
createPass.setPreferredSize(new Dimension(100,100));
JLabel text = new JLabel();
text.setText("<html> Welcome to SECUREPASS! <br> An Extreme Strong Password Generator <br> Developed by OfficialCode");
text.setPreferredSize(new Dimension(150,150));
text.setFont(size);
field = new TextField(20);
field.setSize(new Dimension(50,50));
start = new JFrame("Secureword | Strong password Generator | Coded by OfficialCode");
start.setPreferredSize(new Dimension(390,390));
start.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
start.setLocationRelativeTo(null);
start.setLayout(new BorderLayout());
start.getContentPane().add(createPass, BorderLayout.WEST);
start.getContentPane().add(text, BorderLayout.PAGE_START);
start.getContentPane().add(field, BorderLayout.CENTER);
start.pack();
start.setVisible(true);
password = "";
createPass.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
field.setText(null);
field.selectAll();
allrandom();
}});
}
public static void allrandom() {
String[] pass = new String[8];
Random r = new Random();
for(int i = 0 ; i < pass.length ; i++) {
int ch = 0;
ch = r.nextInt(3);
switch(ch) {
case 1:
if(passsettings.isIfDots()) {
String newchar = "";
newchar = dotpass();
pass[i] = newchar;
break;
}
case 2:
if(passsettings.isIfNum()) {
String newchar2 = "";
newchar2 = Numpass();
pass[i] = newchar2;
break;
}
case 3:
String newchar3 = "";
newchar3 = charchose();
pass[i] = newchar3;
break;
}
}
for(int i = 0 ; i < pass.length ; i++) {
String newpasschar = "";
newpasschar = pass[i];
password = password + newpasschar;
}
field.setText(password);
// random() end
}
public static String uppercasepass() {
Random r = new Random();
String passletter = "";
int rN3 = 0;
rN3 = r.nextInt(26);
switch(rN3) {
case 1:
passletter = "A";
case 2:
passletter = "B";
case 3:
passletter = "C";
case 4:
passletter = "D";
case 5:
passletter = "E";
case 6:
passletter = "F";
case 7:
passletter = "G";
case 8:
passletter = "H";
case 9:
passletter = "I";
case 10:
passletter = "J";
case 11:
passletter = "K";
case 12:
passletter = "L";
case 13:
passletter = "M";
case 14:
passletter = "N";
case 15:
passletter = "O";
case 16:
passletter = "P";
case 17:
passletter = "Q";
case 18:
passletter = "R";
case 19:
passletter = "S";
case 20:
passletter = "T";
case 21:
passletter = "U";
case 22:
passletter = "V";
case 23:
passletter = "W";
case 24:
passletter = "X";
case 25:
passletter = "Y";
case 26:
passletter = "Z";
}
return passletter;
// uppercase() end
}
public static String lowercasepass() {
Random r = new Random();
String passletter = "";
int rN3 = 0;
rN3 = r.nextInt(26);
switch(rN3) {
case 1:
passletter = "a";
case 2:
passletter = "b";
case 3:
passletter = "c";
case 4:
passletter = "d";
case 5:
passletter = "e";
case 6:
passletter = "f";
case 7:
passletter = "g";
case 8:
passletter = "h";
case 9:
passletter = "i";
case 10:
passletter = "j";
case 11:
passletter = "k";
case 12:
passletter = "l";
case 13:
passletter = "m";
case 14:
passletter = "n";
case 15:
passletter = "o";
case 16:
passletter = "p";
case 17:
passletter = "q";
case 18:
passletter = "r";
case 19:
passletter = "s";
case 20:
passletter = "t";
case 21:
passletter = "u";
case 22:
passletter = "v";
case 23:
passletter = "w";
case 24:
passletter = "x";
case 25:
passletter = "y";
case 26:
passletter = "z";
}
return passletter;
}
public static String Numpass() {
Random r = new Random();
String passletter = "";
int rN = 0;
rN = r.nextInt(9);
switch(rN) {
case 1:
passletter = "1";
case 2:
passletter = "2";
case 3:
passletter = "3";
case 4:
passletter = "4";
case 5:
passletter = "5";
case 6:
passletter = "6";
case 7:
passletter = "7";
case 8:
passletter = "8";
case 9:
passletter = "9";
}
return passletter;
}
public static String dotpass() {
Random r = new Random();
String passletter = "";
int rN5 = 0;
rN5 = r.nextInt(5);
switch(rN5) {
case 1:
passletter = "_";
case 2:
passletter = "]";
case 3:
passletter = "$";
case 4:
passletter = "#";
case 5:
passletter = "=";
}
return passletter;
}
public static String charchose() {
Random r = new Random();
String line = "";
int rN = 0;
rN = r.nextInt(20);
switch(rN) {
case 1:
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
case 9:
case 10:
if(passsettings.isIfLowercase()) {
line = lowercasepass();
}
case 11:
case 12:
case 13:
case 14:
case 15:
case 16:
case 17:
case 18:
case 19:
case 20:
if(passsettings.isIfUpprcase()) {
line = uppercasepass();
}
}
return line;
}
}

The problem comes from the fact that Random.nextInt(n) return a value between 0-n (exclusive). Your switch case are all wrong by one.
This explain your null since you don't do anything for ch = 0, the String stays at null:
switch(ch){
case 1: ... //symbol
case 2 ... //number
case 3: ... //letter
}
This should be
switch(ch){
case 0: ... //symbol
case 1: ... //number
case 2: ... //letter
}
Some other issues or improvments :
You don't break after a case so you always get the last case executed (well all following case). Resulting in a possibilities of 4 character zZ9= (easy to bruteforce !)
You should use a char[] instead of String[], there is no need of using String to store one character like you do.
Instead of
String s = "a";
you can
char c = 'a';
Reducing the length of the code if you read the next point.
You can reduce your switch by doing some addition like 'a' + r.nextInt(26) to get a value between 'a' to 'z'
For a random symbol, instead of a switch, create a static array of char[] with every character, then get a random value using the size of this array.
Like :
final static char[] symbol = {'#', '#', '-', '\\', '/', '*'};
static getRadomSymbol(){
Random r = new Random();
return symbol[r.nextInt(symbol.length)];
}
Allowing the add of character easily (and reducing again the number of line ;) )

Java switch statement about number

I have a switch statement which works fine, but I feel like it's poorly formatted and redundant(many of the cases do the same thing). How can I improve this?
switch (number) {
case 10: // do 1
break;
case 12: // do 2
break;
case 13: // do 1
break;
case 15: // do 3
break;
case 17: // do 2
break;
case 18: // do 2
break;
}

I guess you can group the cases with the same output together. It is one way to improve this.
switch (number) {
case 10:
case 13:
// do 1
break;
case 12:
case 17:
case 18:
// do 2
break;
case 15:
// do 3
break;
}
break; is used to terminate a case in the switch statement. So, the cases will have same output when there is no break; between them.

You could improve it by removing a few break statement, like this
switch (number) {
case 10:
case 13: // do 1
break;
case 12:
case 17:
case 18: // do 2
break;
case 15: // do 3
break;
}

You may make it a bit more compact like this:
switch (number) {
case 10:
case 13:
System.out.println("do 1 + " + number);
break;
case 12:
case 17:
case 18:
System.out.println("do 2 + " + number);
break;
case 15:
System.out.println("do 3 + " + number);
break;
}
And the last break; is not required in your case but good practice anyways for defensive programming.

You can add default case. When provided cases are not equal to number default statement is executed. Code:
int number = 0;
switch (number) {
case 10: // do 1
break;
case 12: // do 2
break;
case 13: // do 1
break;
case 15: // do 3
break;
case 17: // do 2
break;
case 18: // do 2
break;
default:
System.out.println(number);
}

Input Repeat with same case

After I run this codes, it says BUILD SUCCESSFUL and it stops. What should I do to make it repeat to ask another input with same case? I did read tutorial on several web but I'm not helped by those.
Here's the code:
import java.util.Scanner;
public class SwitchTry {
public static void main(String[] args) {
int mth;
String mthString;
Scanner scanner = new Scanner(System.in);
mth =scanner.nextInt();
switch (mth) {
case 1: mthString = "January";
break;
case 2: mthString = "February";
break;
case 3: mthString = "March";
break;
case 4: mthString = "April";
break;
case 5: mthString = "May";
break;
case 6: mthString = "June";
break;
case 7: mthString = "July";
break;
case 8: mthString = "August";
break;
case 9: mthString = "September";
break;
case 10: mthString = "October";
break;
case 11: mthString = "November";
break;
case 12: mthString = "December";
break;
default: mthString = "Error";
break;
}
System.out.println(mthString);
}
}
I appreciate any help that you can provide.

I would try using a while loop to encase the switch. So it keeps asking your input.
import java.util.Scanner;
public class SwitchTry {
public static void main(String[] args) {
while(true){
int mth;
String mthString;
Scanner scanner = new Scanner(System.in);
mth =scanner.nextInt();
switch (mth) {
case 1: mthString = "January";
break;
case 2: mthString = "February";
break;
case 3: mthString = "March";
break;
case 4: mthString = "April";
break;
case 5: mthString = "May";
break;
case 6: mthString = "June";
break;
case 7: mthString = "July";
break;
case 8: mthString = "August";
break;
case 9: mthString = "September";
break;
case 10: mthString = "October";
break;
case 11: mthString = "November";
break;
case 12: mthString = "December";
break;
default: mthString = "Error";
break;
}
System.out.println(mthString);
}
}
}

As suggested by MadProgarmmer do-while loop is the perfect use-case for such scenarios. You need to wrap your input line plus switch cases and print statement inside the do-while loop as follow:
do {
//so you know that terminal is asking for input
System.out.println("Input: ");
mth =scanner.nextInt();
//copy/paste your switch case with last System.out.println() here
} while (true);
I am worried about having execution that never ends. Maybe you want to end the loop when the user supplies -1, so change the while(true) to while (mth != -1) and that should be your termination input.

Switch statement always selects same case [duplicate]

This question already has answers here:
If-else working, switch not [duplicate]
(9 answers)
In a switch statement, why are all the cases being executed?
(8 answers)
Closed 8 years ago.
For the following switch statement:
if a value between 0-9 is selected, output is fine. If value greater than 9 is selected, output is always a lowercase z.
for (int i = 0; i < 3; i++)
{
random[i] = randomnumber.nextInt(36);
if (random[i] > 9)
{
switch(random [i])
{
case 10: character[i] = "A";
case 11: character[i] = "B";
case 12: character[i] = "C";
case 13: character[i] = "D";
case 14: character[i] = "E";
case 15: character[i] = "F";
case 16: character[i] = "G";
case 17: character[i] = "H";
case 18: character[i] = "I";
case 19: character[i] = "J";
case 20: character[i] = "K";
case 21: character[i] = "L";
case 22: character[i] = "M";
case 23: character[i] = "N";
case 24: character[i] = "O";
case 25: character[i] = "P";
case 26: character[i] = "Q";
case 27: character[i] = "R";
case 28: character[i] = "S";
case 29: character[i] = "T";
case 30: character[i] = "U";
case 31: character[i] = "V";
case 32: character[i] = "W";
case 33: character[i] = "X";
case 34: character[i] = "Y";
case 35: character[i] = "Z";
}
}
else
character[i] = Integer.toString(random[i]);

A case statement is a form of standidised goto statement, it goes to the case statement and then continues on as usual. To get the behaviour you desire you need a
break;
at the end of each case

Where is the break of the cases man!
switch(random[i]){
case 10: ....
break;
case 11: ....
break;
//and so on
}

Add break with all case blocks like
case 10:
character[i] = "A";
break;