Thread: Beginner for loop

Hi guys

I'm having a bit problem with my for-loop, and would just want to hear if i'm way of, or if there is something small i'm missing.

String[] days = {"Monday", "Tuesday", "Wednesday", "Turshday", "Friday", "Saturday", "Sunday"};
String opgType = arbejdsOpgaver.opgTypeText.getText();
String opgave = arbejdsOpgaver.opgText.getText();
String dag = arbejdsOpgaver.opgDagText.getText();
String kunde = arbejdsOpgaver.opgKundeText.getText();
 
boolean opgCheck = false;
			if (!opgave.equals("") && opgave.charAt(0) != ' ') {
				if (!dag.equals("") && dag.charAt(0) != ' ') {
					if (!kunde.equals("") && kunde.charAt(0) != ' ') {
						opgCheck = true;					
					}
				}
			}
 
			if (opgCheck == true) {
				try {
					String day = null;
					for (int i=0; i<= days.length; i++) {
						day.equals(day + days[i]);
							if (!day.equals(days)) {
								opgCheck = false;
							}
					}
				}catch (Exception ee) {
					System.out.println(ee);
				}	
			}

I want the for-loop to run through the array, and if the entered day doesn't match one of the days in the array, make the check = false.

At the moment it obviously doesn't work because i'm getting an exception:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at ajRengøring.logic.createOpgave.actionPerformed(cre ateOpgave.java:32)
at javax.swing.AbstractButton.fireActionPerformed(Unk nown Source)
at javax.swing.AbstractButton$Handler.actionPerformed (Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed (Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseRe leased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent( Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(U nknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unkno wn Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPri vilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPri vilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPri vilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilter s(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(U nknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

What is line 32?

Line 32 is:

day.equals(day + days[i]);

I can see where you are going, and it solved a problem I probably would have run into at some point (Removed the =). But it does not solve the problem itself. I tried to change a bit in that line 32, which got rid of the exception, but it doesn't seem to really run through the array, or at least not adding the content of the array to the string?

String[] days = {"Monday", "Tuesday", "Wednesday", "Turshday", "Friday", "Saturday", "Sunday"};
String opgType = arbejdsOpgaver.opgTypeText.getText();
String opgave = arbejdsOpgaver.opgText.getText();
String dag = arbejdsOpgaver.opgDagText.getText();
String kunde = arbejdsOpgaver.opgKundeText.getText();
 
boolean opgCheck = false;
			if (!opgave.equals("") && opgave.charAt(0) != ' ') {
				if (!dag.equals("") && dag.charAt(0) != ' ') {
					if (!kunde.equals("") && kunde.charAt(0) != ' ') {
						opgCheck = true;					
					}
				}
			}
 
			if (opgCheck == true) {
				try {
					String day = null;
					for (int i=0; i<= days.length; i++) {
						day += days[i]; // previously day.equals(day + days[i]);
							if (!day.equals(days)) {
								opgCheck = false;
							}
					}
				}catch (Exception ee) {
					System.out.println(ee);
				}	
			}

		String[] days = { "Monday", "Tuesday", "Wednesday", "Turshday", "Friday", "Saturday", "Sunday" };
		String day = "";
		for (int i = 0; i < days.length; i++) {
			day += days[i]; // previously day.equals(day + days[i]);
		}
		System.out.println(day);

This is working fine, so i think it might be something else in your code.
Also try to switch your String day = null to String day = ""; If it still doesnt work then try printing everything out.

Yeah I can also print it. But the if statement somehow doesn't wanna work. Pitty since I now need to test for the days individually so it says Monday OR Tuesday etc. It just doesn't look good that way.

Well, the end product should be to add data to a database. This particular part of the class is supposed to check whether the entered input is a valid day. In other words the program should go: Is it a monday? No, is it a Tuesday? No etc until the entered data matches one in the array, and it continues in the code.

The class as it looks at the moment.

public class createOpgave implements ActionListener {
	public void actionPerformed(ActionEvent e) {
		String[] days = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};
		String opgType = arbejdsOpgaver.opgTypeText.getText();
		String opgave = arbejdsOpgaver.opgText.getText();
		String dag = arbejdsOpgaver.opgDagText.getText();
		String kunde = arbejdsOpgaver.opgKundeText.getText();
 
		if (opgType.equals("Privat")) {
			boolean opgCheck = false;
			if (!opgave.equals("") && opgave.charAt(0) != ' ') {
				if (!dag.equals("") && dag.charAt(0) != ' ') {
					if (!kunde.equals("") && kunde.charAt(0) != ' ') {
						opgCheck = true;					
					}
				}
			}
 
			if (opgCheck == true) {
				String day = "";
					for (int i=0; i< days.length; i++) {
						if (!dag.equals(day)) {
							opgCheck = false;
							day += days[i];
						}
					}
			}	
			if (opgCheck == true) {				
					try{
						connect.forbindelse();
						//SQL kaldet laves til at indsætte i afdelingtabellen
						String priOpg = ("INSERT INTO opgaverPrivat VALUES(null,'"+opgave+"','"+dag+"','"+kunde+"')");
						connect.st.executeUpdate(priOpg);
						JOptionPane.showMessageDialog(null, "Registered");
 
						}catch (Exception ee) {
							System.out.println(ee);
						}
				} else
				JOptionPane.showMessageDialog(null, "Error");			
		}

Apart from that it only getText from some gui component in another class.

String day = "";
					for (int i=0; i< days.length; i++) {
						if (!dag.equals(day)) {

This part, what should it do?

Originally Posted by elamre

String day = "";
					for (int i=0; i< days.length; i++) {
						if (!dag.equals(day)) {

This part, what should it do?

The code should probably look like this:

String day = "";
					for (int i=0; i< days.length; i++) {
                                                day += days[i];
						if (!dag.equals(day)) {

That obviously doesn't do what I want because that's the part that doesn't work. But that is the day check. The plan is to run through the array with the loop, and for every content(day) of the array check for whether that is the entered input in my textfield(dag). If it doesn't matches set the check = false. Since it was true at the beginning of the loop it shouldn't be necessary to change the check if it matches.

I do see a problem coming up if the current problem is solved, because if you enter Monday it will match, but the loop will continue on and override the String and make it false anyway. So somehow it should also break out if it matches. But at the moment it doesn't work even with Sunday so it can't be that problem.

In other words the check should be the same as this one at the top, where I individually check for every day:

if (opgCheck == true) {
				if (dag.equals("Monday") || dag.equals("Tuesday") || dag.equals("Wednesday") || dag.equals("Thursday")	|| dag.equals("Friday") || dag.equals("Saturday") || dag.equals("Sunday")) {
					try{
						connect.forbindelse();
						//SQL kaldet laves til at indsætte i afdelingtabellen
						String priOpg = ("INSERT INTO opgaverPrivat VALUES(null,'"+opgave+"','"+dag+"','"+kunde+"')");
						connect.st.executeUpdate(priOpg);
						JOptionPane.showMessageDialog(null, "Opgave registeret");
 
						}catch (Exception ee) {
							System.out.println(ee);
						}