What is a Constructor in Java? In Java, a constructor is a special type of method that is used to initialize objects. When you create an object of a class, the constructor is called automatically. Its main job is to set the initial values of the object’s properties or perform any setup that the object needs before it can be used. Why Do We Need Constructors? You need constructors because: Initialization : Constructors are responsible for initializing an object when it is created. Automatic Execution : A constructor is automatically called when an object is created, so you don’t have to manually initialize every property. Simplifying Object Creation : It simplifies object creation by providing default values or custom initialization. Where Do Constructors Fit in Java? Constructors fit within a class. They are used whenever a new object of that class is created, and they allow the object to be initialized. Constructors must have the same name as the class, and they don't have a re...
In Java, the `throw` statement is used to explicitly throw an exception within a method or block of code. It is typically used when an exceptional condition occurs that the method cannot handle itself, and it wants to signal to the calling code that something went wrong.
Syntax:
throw throwableObject;
Explanation:
- The `throw` statement requires an argument, which is usually an instance of a subclass of `Throwable` (either an exception or an error).
- The argument passed to `throw` can be any expression that results in a throwable object.
- When a `throw` statement is executed, the program flow is immediately transferred out of the current method or block and back to the calling code.
- The caller can then catch the thrown exception using a `try-catch` block or propagate it further up the call stack.
Example:
public class AgeValidator {
public static void validateAge(int age) {
if (age < 0) {
throw new IllegalArgumentException("Age cannot be negative");
}
if (age < 18) {
throw new RuntimeException("Must be at least 18 years old");
}
System.out.println("Age is valid");
}
public static void main(String[] args) {
try {
validateAge(20);
validateAge(-5); // This will throw an IllegalArgumentException
} catch (IllegalArgumentException e) {
System.out.println("IllegalArgumentException: " + e.getMessage());
} catch (RuntimeException e) {
System.out.println("RuntimeException: " + e.getMessage());
}
}
}
In this example, the `validateAge` method throws either an `IllegalArgumentException` or a `RuntimeException` based on the age provided. The `main` method catches these exceptions and prints appropriate error messages.
Analogy:
Imagine you are a lifeguard at a swimming pool. When you see someone struggling in the water (an exceptional condition), you throw a lifeline or buoy (an exception) to help them. The lifeline indicates to others that there is a problem and needs attention. Similarly, when an exceptional condition occurs in a Java program, the `throw` statement signals to the calling code that something unexpected has happened and needs to be addressed.
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