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Object Oriented Programming Articles
Page 330 of 589
What happens when we try to add a duplicate key into a HashMap object in java?
No, HashMap does not allow duplicate keys. The HashMap is a class that implements the Map interface. It is based on the Hash table. It is used to store key-value pairs. It allows null keys and values, but it does not allow duplicate keys. You can store key-value pairs in the HashMap object. Once you do so, you can retrieve the values of the respective keys, but the values we use for keys should be unique. Let's understand what will happen if we try to add a duplicate key into a HashMap.Addng a duplicate key to a HashMapThe put() method ...
Read MoreReading data from keyboard using console class in Java
The Console class is part of the Java.io package and is used to read input from the keyboard or user and write output to the console. Unlike Scanner, the Console class provides methods to read text and passwords. If you read a password using the Console class, it will not be displayed to the user (without showing the typed characters). To use the Console class, we need its object, and the Console object is obtained by calling System.console() as shown below - Console console = System.console(); Note: If you try to execute the program in a non-interactive environment like an IDE, it doesn’t work. It ...
Read MoreHow to set a tooltip text for each item of a JList in Java?
In this article, we will learn to set a tooltip text for each item of a JList in Java. Tooltips give meaningful information as users hover over UI components. Swing's JList does not support tooltips on a per-item basis, so it will involve some customization. What is JList? A JList is a subclass of the JComponent class, and it can be used to display a list of objects that allows the user to select one or more items. A JList can generate a ListSelectionListener interface and needs to implement the abstract method valueChanged(). Syntax The following is the syntax for ...
Read MoreHow to Write/create a JSON file using Java?
In this article, we will learn to write/create a JSON file using Java. JSON has become the standard for data exchange for any kind of application. Java also has a collection of libraries helpful in creating and storing JSON files. JSON JSON or JavaScript Object Notation is a lightweight text-based open standard designed for human-readable data interchange. Conventions used by JSON are known to programmers, which include C, C++, Java, Python, Perl, etc. Sample JSON document Below is an example of a JSON file: { "book": [ { ...
Read MoreWhat are cin, cout and cerr streams in C++?
The cin, cout, cerr, and clog are streams that handle standard input and output stream objects, which are defined in an header file. Standard Output Stream (std::cout) The cout is an object of class ostream that represents the standard output stream oriented to narrow characters (of type char). It corresponds to the C stream stdout. The standard output stream is the default destination of characters determined by the environment. This destination may be shared with more standard objects (such as cerr or clog). Syntax Here is the following syntax for cout in C++: cout
Read MoreWhen will be an IllegalStateException (unchecked) thrown in Java?
In this article, we will learn how an IllegalStateException (unchecked) is thrown in Java. IllegalStateException is a subclass of RuntimeException. It occurs when a method is used at the wrong time or when an object is not in the right state. What is an IllegalStateException? An IllegalStateException is an unchecked exception in Java. This exception may arise in our Java program mostly if we are dealing with the collection framework of java.util.package. There are many collections, such as List, Queue, Tree, and Map, of which List and Queues (Queue and Deque) throw this IllegalStateException under particular conditions. When will ...
Read MoreConvert List of Characters to String in Java
In this article, we will learn to convert a list of characters to strings in Java. Sometimes, when we handle character-based data structures, we need to convert a list of characters into a string. Problem Statement Given a list of characters, the task is to convert it into a single string where the order of characters remains unchanged. Input: list = Arrays.asList('W', 'e', 'l', 'c', 'o', 'm', 'e'); Output: Welcome Methods to Convert a List of Characters to a String The following are the different approaches to convert a list of characters to a string in Java - ...
Read MoreWhat is the difference between cerr and clog streams in c++?
cerr and clog are both objects of the stderr(standard error) stream, which is used to display error messages or diagnostics. In this article, we will learn the difference between these two in more detail. Further, the description of the cout object is also given to get a clearer picture. Unbuffered standard error stream (cerr) The cerr is the standard error stream, which is used to output the errors. This is also an instance of the ostream (as iostream means input/output stream) class. As cerr is unbuffered, therefore it's used when we need to display the error message instantly. It doesn't ...
Read MoreHow can we set a border to JCheckBox in Java?
In this article, we will learn to set a border for JCheckBox in Java. JCheckBox is a Swing component that is commonly used in user interface selection. Although it includes a default appearance, we can customize its look by setting borders in order to have a good visual effect. What is a JCheckBox? A JCheckBox is a component that extends JToggleButton, and an object of JCheckBox represents an option that can be checked or unchecked. Syntax The following is the syntax for JCheckBox initialization: JCheckBox Checkbox_name = new JCheckBox(); If there are two or more options, then any ...
Read MoreHow can we set the shortcut key to a JButton in Java?
In this article, we will learn to set the shortcut key to a JButton in Java. In Swing-based applications, we can implement the addition of keyboard shortcuts to buttons to enable quicker navigation by the user. What is a JButton? A JButton is a subclass of AbstractButton, and it can be used to add platform-independent buttons to a Java Swing application. When the button is pressed or clicked, a JButton can generate an ActionListener interface; it can also generate the MouseListener and KeyListener interfaces. Setting the Shortcut Key for JButton We can also set the shortcut keys for a JButton ...
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