Why does newInstance() return null?

问题:

According to the JavaDocs, the newInstance() Method of java.lang.Class is not intented to return null. But my code seems to prove the opposite. Why?

public Assessment createAssessment() {
    Class<? extends Assessment> assessmentClass = (Class<? extends Assessment>) assessmentClassDataTable.getRowData();
    try {
        System.out.println("ASSESSMENTCLASS " + assessmentClass);
        // -> 'ASSESSMENTCLASS class my.model.ManualSelectAssessment'
        Assessment a = assessmentClass.newInstance();
        System.out.println("ASSESSMENT " + a);
        // -> 'ASSESSMENT null'
        return a;
    } catch (Exception e) {
        Application.handleError(e);
    }
    return null;
}

It returns null.

回答1:

newInstance() never returns null. However newInstance().toString() can return "null"

Note: One gotcha with newInstance() is that it can throw a CheckedException !

public Main() throws IOException {
    throw new IOException();
}

public static void main(String[] args) throws InstantiationException, IllegalAccessException {
    Main.class.newInstance(); // throws IOException silently.
}

Even though IOException is a check exception, the compiler has not idea the newInstance() will throw this checked exception. If you try to catch it the compiler will complain it cannot be thrown !!