Short-circuit evaluation means Java stops checking a logical expression as soon as it knows the final result. With &&, if the left side is false, the right side never runs. With ||, if the left side is true, the right side never runs.
This is not just a performance detail. You can use it to guard against errors.
String name = null;
if (name != null && name.length() > 0) {
System.out.println(name);
}
Without short-circuiting, name.length() would crash with a NullPointerException because you cannot call methods on null. But since name != null is false, Java skips the second condition entirely. This pattern shows up in production code constantly.