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How do I resize the text inside my JScrollpane - JAVA

I'm currently learning more about Java. I'm working on creating a GUI which is able to 'translate' amino-acid characters into their 3-letter codes.
I've got everything working as intended, but I'm still struggling to understand how I can resize the text inside my JScrollpane to not exceed the width. (Example in picture)
Do I just need to change some settings or maybe add '\n's to fit the JTextArea? Here's the code:
Thanks in advance!
private void createGUI() {
Container window = this.getContentPane();
window.setLayout(new FlowLayout());
panel = new JPanel();
inputField = new JTextField();
startButton = new JButton("Convert to 3-letter code");
display = new JTextPane();
scroll = new JScrollPane(display);
//CUSTOMIZE GUI OBJECTS
inputField.setPreferredSize(new Dimension(200, 20));
display.setPreferredSize(new Dimension(400, 300));
startButton.addActionListener(this);
//SETTING UP TEXTAREA
display.setEditable(false);
scroll.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
scroll.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
panel.setLayout(new BorderLayout());
panel.add(scroll, BorderLayout.CENTER);
//
window.add(inputField);
window.add(startButton);
window.add(panel);
}

Better use a JTextArea instead of a JScrollPane since the best that the JScrollPane can do is to dynamically resize (Dynamically Resize a JScrollPane?)

I changed JTextPane display to a JTextArea object and changed 'display.setLineWrap(true);'
This fixed the issue I was having with JTextPane.

To answer the question in the title: How do I resize the text inside my JScrollpane
Inside your scrollpane you have some JComponent. Either that JComponent is fully visible since it is smaller or equal to the JScrollpane's viewport. Or it is bigger, in which case the JScrollpane will start displaying scrollbars and the relevant part.
To resize the text you will just have to tell the JComponent inside the JScrollpane to display the text differently. Depending on the JComponent you use this method may vary. Here some examples:
In a JLabel and most other components, increase the font size (How to change the size of the font of a JLabel to take the maximum size)
In a JLabel, switch to a multiline label (Multiline text in JLabel)
In a JTextArea, turn on word wrapping and line wrapping
In a JEditorPane you can even use markup inside the document to use different font sizes at the same time

How to fill JFrame window with a JPanel?

I am trying to set a JPanel fill the whole window of a JFrame. The layout of JPanel is GridBagLayout. If i change it to BorderLayout it works. But i need the GridBagLayout and in this way the JPanel appears on the Center of the window.
How can i fill the whole window of JFrame with the JPanel( just like with BorderLayout )?

First, make sure you read How to Use GridBagLayout
Next, make sure you have the JavaDocs for GridBagConstraints open and available
These two basic references will provide you with 99% of the information you need to answer just about most of you issues.
Without more context, something like...
GridBagConstraints gbc = new GridBagConstraints();
gbc.weightx = 1;
gbc.weighty = 1;
gbc.fill = GridBagConstraints.BOTH;
will achieve the result you're looking for
Remember though, you are not stuck to a single layout manager, you can use multiple containers all using different layout managers to achieve your desired results

Java how to preserve newline from String to JLabel?

JLabel newLabel = new JLabel();
String a = b;//b is String from database.
newLabel.setText(a);
I need to generate text pulled from my database which contains multiple line, but when i put them into the label, all of the text became same line.
I tried using JTextArea and it works, however, for some reason it messed with all the other component's alignment in a 1 column BoxLayout panel... which I wanted all the content to be aligned to the left. Any help would be much appreciated! thanks

however, for some reason it messed with all the other component's alignment in a 1 column BoxLayout panel
The is related to the setAlignmentX(...) method of each component.
A JLabel uses 0.0f (for left alignment). A JTextArea and JScrollPane use 0.5f (for center alignment).
Using components with different alignments will cause alignment issues when using a BoxLayout.
The solution is to change the alignment of the text area or scroll pane (whichever component you add to the BoxLayout).
So the basic code would be:
JLabel label = new JLabel(...);
JTextArea textArea = new JTextArea(...);
textArea.setAlignmentX(0.0f);
JPanel panel = new BoxLayout(...);
panel.add(label);
panel.add(textArea);
Now both components will be left aligned.

GridBagLayout one cell alignment for label

I have for example 3x3 components in grid layout, and I would like all of them to be labels, but since I have some padding I want my labels to be in center of their cell. But I can't seem to manage it...
Part of the relevant code:
panel = new JPanel();
GridBagLayout gridBag = new GridBagLayout();
panel.setLayout(gridBag);
panel.setSize(new Dimension(30, 400));
GridBagConstraints c = new GridBagConstraints()
JLabel lab = new JLabel("proba");
lab.setBorder(outline);
c.fill = GridBagConstraints.BOTH;
c.gridx =2; c.gridy=2; c.ipady = 10; c.ipadx=10;
c.ipadx=100; panel.add(lab,c);

[update]
You really should post an SSCCE so we can all try it and not have to guess where the problem is. My last guess - and this is something you should do regardless of whether it fixes your current problem - is
label.setHorizontalAlignment(JLabel.CENTER);
If your label is centered and fills the entire grid cell, the text will still be left justified by default. The above change will cause the text to be centered within the label.
However if your label is not filling the cell, this won't help.
[original]
It's hard to say exactly what's wrong since this is not a full program, but here are a few comments that might get you on the right track.
First, you should be using setPreferredSize instead of setSize (see Java: Difference between the setPreferredSize() and setSize() methods in components)
When you make this change you will see that the panel is not quite what you want. It's very tall and thin. Perhaps a typo - did you mean (300,400) instead of (30,400)
Now I'm guessing all your labels will be clumped together. In order to get them to spread out you need to add:
c.weightx = .5;
c.weighty = .5;
(actually any non-zero value will work). This is described in http://docs.oracle.com/javase/tutorial/uiswing/layout/gridbag.html
Unless you specify at least one non-zero value for weightx or weighty, all the components clump together in the center of their container. This is because when the weight is 0.0 (the default), the GridBagLayout puts any extra space between its grid of cells and the edges of the container.
This should get you close(r) ...

How to reduce the space between the 3 swing checkboxes?

I want to reduce the size between the components with in the Formatting group (left side on the image). How to do this?
JPanel formattingGroup = createGroupWithName("Formatting");
formattingGroup.setMinimumSize(new Dimension(250, 20));
formattingGroup.setLayout(new GridLayout(5, 0));
add(formattingGroup);
final JCheckBox showSurface = new JCheckBox("Show surface");
showSurface.setSelected(true);
formattingGroup.add(showSurface);
final JCheckBox showTerrain = new JCheckBox("Show terrain");
showTerrain.setSelected(true);
formattingGroup.add(showTerrain);
final JCheckBox showVehicleStatus = new JCheckBox("Show vehicle status");
showVehicleStatus.setSelected(true);
formattingGroup.add(showVehicleStatus);
JPanel pnl = createGroupWithName("Depth Stretch");
formattingGroup.add(pnl);
JSlider slider = new JSlider(0, 10);
pnl.add(slider);

When using a GridLayout all components are made the same size.
You are adding a JPanel with a TitledBorder and a JSlider to the grid. Therefore the checkboxes will take the same vertical height as that panel.
You need to use a different layout manager for the panel. Maybe a vertical BoxLayout.

You might look at available size variants, discussed in Resizing a Component.

Use gridbaglayout because that gives you the opportunity to give weights, to columns or rows and set spacing and padding values.
I made a Swing application that contains out of 12 Frames and they all are made with GridBagLayout.
I also tried other before that but they all had limits. That's where the GridBagLayout kicks in. It's a bit harder in begin to understand how it works, but once you get feeling with it, it really is best thing to get the components where you want.
If you want i'll give you a cool example of a frame created with GridBagLayout.