国产ef卡口镜头推荐 Java Errors

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Even experienced Ja developers make mistakes. The key is learning how to spot and fix them!

These pages cover common errors and helpful debugging tips to help you understand what's going wrong and how to fix it.

Types of Errors in Ja Error Type Description Compile-Time Error Detected by the compiler. Prevents code from running. Runtime Error Occurs while the program is running. Often causes crashes. Logical Error Code runs but gives incorrect results. Hardest to find. Common Compile-Time Errors

Compile-time errors occur when the program cannot compile due to syntax or type issues.

Here are some examples:

1) Missing Semicolon

Example int x = 5 System.out.println(x);

Result:

error: ';' expected

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Tip: Ja requires a semicolon at the end of every statement (int x = 5;).

2) Undeclared Variables

Example System.out.println(myVar);

Result:

cannot find symbol   symbol: variable myVar

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Tip: You must declare a variable before using it (int myVar = 50;).

3) Mismatched Types

Example int x = "Hello";

Result:

incompatible types: String cannot be converted to int

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Tip: Make sure the value matches the variable type (String x = "Hello";).

Common Runtime Errors

Runtime errors occur when the program compiles but crashes or behes unexpectedly.

Here are some examples:

1) Division by Zero

Example int x = 10; int y = 0; int result = x / y; System.out.println(result);

Result:

Exception in thread "main" ja.lang.ArithmeticException: / by zero

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2) Array Index Out of Bounds

Example int[] numbers = {1, 2, 3}; System.out.println(numbers[8]);

Result:

Exception in thread "main" ja.lang.ArrayIndexOutOfBoundsException: Index 8 out of bounds for length 3

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Logical Errors

Logical errors happen when the code runs, but the result is not what you thought:

Example: int x = 10; int y = 2; int sum = x - y; System.out.println("x + y = " + sum);

Result:

x + y = 8

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Expected Result: 12

Logical Error: The code mistakenly subtracts instead of adds.

Tip: Test your program with different inputs to catch logic flaws (try using x + y instead). This is part of debugging, which you will learn more about in the next chapter.

Good Habits to Avoid Errors Use meaningful variable names Read the error message carefully. What line does it mention? Check for missing semicolons or braces Look for typos in variable or method names

In the next chapter, you will learn how to debug your code - how to find and fix bugs/errors in your program.

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