in java throw,what,why?

In Java, throw is a keyword used to explicitly throw an exception. Here's a breakdown of the what, why, how, and when to use it:

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🔹 What is throw in Java?

• throw is used to manually trigger an exception during program execution.
• It transfers control from the current block of code to the nearest catch block that can handle the exception.

throw new IllegalArgumentException("Invalid input");

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🔹 Why use throw?

You use throw to:

• Handle unexpected situations or errors in your code.
• Validate input (e.g., null values, invalid arguments).
• Provide custom error messages or throw custom exceptions.
• Improve code robustness by catching problems early.

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🔹 How to use throw in Java?

✅ Syntax:

throw new ExceptionType("Error message");

✅ Example:

public void setAge(int age) {
    if (age < 0) {
        throw new IllegalArgumentException("Age cannot be negative");
    }
    this.age = age;
}

Note: The object thrown must be of type Throwable (i.e., Exception or subclass).

✅ Custom Exception Example:

class MyException extends Exception {
    public MyException(String message) {
        super(message);
    }
}

public void checkSomething(boolean condition) throws MyException {
    if (!condition) {
        throw new MyException("Condition failed");
    }
}

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🔹 When to use throw in Java?

Use throw when:

• You need to stop normal flow due to a problem.
• Input is invalid or violates rules.
• Something unexpected happens (e.g., file not found, null value).
• You are implementing custom business logic exceptions.

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⚠️ Common Mistakes

• Forgetting new when creating the exception:

  throw IllegalArgumentException("error"); // ❌ wrong
  throw new IllegalArgumentException("error"); // ✅ correct

• Throwing a non-Throwable type:

  throw "error"; // ❌ wrong

• Forgetting to declare or handle checked exceptions:

  public void riskyMethod() throws IOException {
      throw new IOException("Disk not found"); // must declare or handle
  }

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Would you like an explanation of the difference between throw and throws too?