In what scenarios does the AssertionError exception in Java occur?

In what scenarios does the AssertionError exception in Java occur?

In the Java language, assertions are a mechanism used to test assumptions during development. They have the function of checking whether the code assumptions are true. When the assertion fails, the system will throw an AssertionError exception.

AssertionError exception usually occurs under the following circumstances:

1. Assertion check failed

If we use the assert keyword, then when it is added When the expression does not hold, the program will throw an AssertionError exception. For example, the following code:

int a = 1;
assert a == 0 : "a的值不是0";

When a is not equal to 0, the program will throw an AssertionError exception, prompting "the value of a is not 0".

2. Type conversion error

In Java, type conversion may also cause the occurrence of AssertionError exception. For example, the following code:

int a = 10;
assert (double)a == 10.0 : "类型转换错误";

When converting the int type to the double type, if the conversion fails, the program will throw an AssertionError exception, prompting "type conversion error".

3. Array out of bounds

When we access an array, an out of bounds exception may occur. Likewise, an AssertionError exception may occur in this case. For example, the following code:

int[] arr = {1,2,3};
assert arr[3] == 5 : "数组越界";

When we try to access the fourth element of the array, since the array only contains 3 elements, the program will throw an AssertionError exception, prompting "array out of bounds".

4. Method parameter checking

When we write a method, we may need to check the incoming parameters to ensure that they meet the requirements. In this case, if the parameters do not meet the requirements, we can use the assert statement to throw an AssertionError exception. For example:

void doSomething(String str){
    assert str != null : "参数不能为空";
    // 程序正常执行
}

If we pass in an empty string, the program will throw an AssertionError exception, prompting "The parameter cannot be empty."

In general, although AssertionError exceptions are relatively rare, we still need to pay attention to the occurrence of such exceptions during the development process in order to troubleshoot and repair code problems in a timely manner.

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