public class TimeoutString implements CharSequence {
    private final CharSequence child;
    private final long target;

    public TimeoutString(CharSequence child, long timeout) {
        this.child = child;
        this.target = System.nanoTime() + timeout*1000000;
    }

    private void checkTarget() {
        if (System.nanoTime() > target)
            throw new IllegalStateException("String operation timeout.");
    }

    @Override
    public int length() {
        checkTarget();
        return child.length();
    }

    @Override
    public char charAt(int i) {
        checkTarget();
        return child.charAt(i);
    }

    @Override
    public CharSequence subSequence(int a, int b) {
        checkTarget();
        return child.subSequence(a, b);
    }
}