如何重写多个三元“？ ：“就”如果“陈述而言？

Question

I understand that:

value = (a > b) ? a : b;

is the same as:

if (a > b)
  value = a;
else
  value = b;

But I'm having trouble deciphering what this means:

EDIT (the previous example I used was not good, this is real code from another example):

Tracker t = (trackerId == TrackerName.APP_TRACKER) ? analytics.newTracker(PROPERTY_ID)
      : (trackerId == TrackerName.GLOBAL_TRACKER) ? analytics.newTracker(R.xml.global_tracker)
          : analytics.newTracker(R.xml.ecommerce_tracker);

How do I rewrite the last equation in terms of if , else if , and else ?

Answer 1

You need a second conditional for this ternary expression to work.

value = (a > b) ? a : (b > c) ? c : d;

Then it would become:

if (a > b) {
    value = a;
} else if (b > c) {
    value = c;
} else {
    value = d;
}

In your case:

if (trackerId == TrackerName.APP_TRACKER) {
    t = analytics.newTracker(PROPERTY_ID);
} else if (trackerId == TrackerName.GLOBAL_TRACKER) {
    t = analytics.newTracker(R.xml.global_tracker);
} else {
    t = analytics.newTracker(R.xml.ecommerce_tracker);
}

Resources:

• Multiple conditions in ternary operators

Answer 2

So based on the example you linked :

Tracker t = (trackerId == TrackerName.APP_TRACKER) ? analytics.newTracker(PROPERTY_ID)
      : (trackerId == TrackerName.GLOBAL_TRACKER) ? analytics.newTracker(R.xml.global_tracker)
          : analytics.newTracker(R.xml.ecommerce_tracker);

Which you seemed to have used to produce value = (a > b) ? a : b ? c : d; value = (a > b) ? a : b ? c : d; , which should probably be more like, value = (a == b) ? c : (a == d) ? e : f value = (a == b) ? c : (a == d) ? e : f value = (a == b) ? c : (a == d) ? e : f , it would read something like...

Tracker t = null;
if (trackerId == TrackerName.APP_TRACKER) {
    t = analytics.newTracker(PROPERTY_ID);
} else if ((trackerId == TrackerName.GLOBAL_TRACKER)) {
    t = analytics.newTracker(R.xml.global_tracker);
} else {
    t = analytics.newTracker(R.xml.ecommerce_tracker);
}

Answer 3

Use an IDE like Eclipse that offers the possibility to automatically rewrite ternary operators as ifs. Ctrl + 1 opens the quick fix shown below.