Adding various type of components into a JComponent reference array

Question

I have a JComponent reference like JComponent allComp[]; Now I want to every element of this array holds different type of component like below,

allComp[0] = new JComboBox();

allComp[1] = new JButton();

allComp[2] = new JMonthChooser();

I am trying and getting Null Pointer exception. Is this possible?? If possible how?? Please help me in this issue. Thanks advance

Answer 1

You probably have not initialized allComp and it's null.

JComponent allComp[] = new JComponent[MAX_COMPONENTS];

Anyway, it is advisable to use a List instead of an array if you don't know beforehand the number of components.

List<JComponent> allComp = new ArrayList<>();
allComp.add(new JComboBox());
allComp.add(new JButton());
allComp.add(new JMonthChooser());

Answer 2

You need to create the array object itself:

JComponent[] allComp = new JComponent[ARRAYSIZE]; 

Answer 3

I assume that you haven't initialized the array

int arraySize = 20;
JComponent allComp[] = new JComponent[arraySize];

Doing something like

JComponent allComp[]

Only "declares" the object, which is sort of like a promise "somewhere in this code I will use this object, but I haven't decided what I want it to be yet, so I'm leaving it undefined".

"Initialization" is what you need to do to actually create the object. Usually you do this with the

new

keyword.