Whether or not to use multiple return statements

moreReadable.java

    private boolean isReadable(String myString) {
        boolean isValid = true;

        // as I expect my string to be valid by default, I only need to check when the string is NOT valid
        // which also means I can get rid of the second if-statement in notReadable.java
        if (myString.length() == 0) {
            isValid = false;
        }

        // ..

        // this bit of code should only be invoked if my string still is valid
        if (isValid) {
            myString = myString.concat("useless");
            isValid = myString.length() < 10;
        }

        return isValid;
    }

notReadable.java

    private boolean isNotReadable(String myString) {
        if (myString.length() == 0) {
            return false;
        }

        if (myString.equals("something")) {
            return true;
        }

        // ..

        // this bit of code should NEVER be reached when previous if-statements evaluated to true
        // ..that assumtion might be clear at that given moment, what in 1 year when your colleague needs to fix a bug?
        // I could easily read this as "always concat useless to my string", but be suprised when looking further up the method
        myString = myString.concat("useless");
        return myString.length() < 10;
    }