Question

Here’s demo,

public class MyClass {
    public MyClass(String str) {
        if (null == str)
            return;

        mStr = processInput(str);
        mMember1 = initMember1();
        // ... some other initialization
}

Something like above, is it good or bad?
If it returned, we may get a constructed object without correct initialization.

Answer 1

It depends.

If your class can behave properly with a null being passed to the constructor and bypassing initialization, then it’s OK.

If your class can’t, throw an exception, if not a checked exception then typically IllegalArgumentException.

It looks as though this constructor is a convenience constructor equivalent to:

MyClass o = new MyClass();
o.doSomethingWithString(str);

If so, a better approach may be to use the fluent interface pattern, where methods return this (where possible), so you can code:

MyClass o = new MyClass().doSomethingWithString(str);

Here, the method doSomethingWithString() instead of being declared as void, has a return type of MyClass and the last line would be return this;. This pattern is handy for chaining up calls to methods, ie o.doX().setY(y).doZ(); etc