throws Clause

throws Clause

1. What It Means (beginner)

throws = warning sign on method: "I MIGHT throw this — caller, handle it!" For checked exceptions (files, SQL — compiler forces!). Like "caution: wet floor" board!

2. Code — File Read Warns!

import java.io.*;
class Demo {
    static void read() throws IOException { // WARNS (passes duty up!)
        BufferedReader br = new BufferedReader(new FileReader("a.txt"));
        System.out.println(br.readLine());
        br.close();
    }
    public static void main(String[] args) {
        try { read(); } // caller handles!
        catch (IOException e) { System.out.println("file missing!"); }
    }
}
// throws IOException, SQLException (many, comma-separated!)

3. throws vs throw (exam table — #1 confusion!)

	throws (with s!)	throw (no s!)
Job	warns (declaration!)	throws actually (action!)
Where	method signature	inside body
Example	void f() throws IOException	throw new ArithmeticException();

4. Rules (traps!)

• Checked exception + no catch + no throws = COMPILE ERROR!
• Unchecked (Arithmetic, NullPointer) need NO throws (optional!).
• Overriding can't add BIGGER checked (child ≤ parent!).

5. Exam Points

• throws program + vs throw table — 5-7 marks, very frequent.
• Checked-needs-throws — 3 marks, frequent.