Oracle Certified Professional: Java SE 17 Developer (1Z0-829) Practice Tests

Explanation

The + operator is evaluated strictly left to right and switches behavior when it encounters a String operand. In the first statement, 1 + 2 is processed first as integer addition producing the int 3, then 3 + "3" triggers string concatenation to produce "33". In the second statement, "1" + 2 triggers string concatenation immediately because the left operand is already a String, producing "12", then "12" + 3 concatenates to produce "123". Once a String operand appears on the left, all subsequent + operators in that left-to-right chain become concatenation rather than addition.

Explanation

Java caches Integer instances for values in the range -128 to 127 inclusive. When Integer a = 100 and Integer b = 100 are assigned, both variables point to the same cached object, so the == operator compares the same reference and returns true. Integer c = 200 and Integer d = 200 fall outside the cache range, so the JVM creates two separate Integer objects. The == operator compares references, not values, so c == d returns false. The output is therefore true false. To compare integer values reliably regardless of range, equals() should be used instead of ==. This caching behavior is an implementation detail guaranteed by the Java Language Specification only for the range -128 to 127.

Explanation

Arrays.binarySearch() requires the array to already be sorted in ascending order. When the target element is present, the method returns its index. When the element is absent, it returns -(insertion point) - 1, where the insertion point is the index at which the value would need to be inserted to maintain sorted order. For the value 25, it falls between 20 at index 1 and 30 at index 2, so the insertion point is 2 and the return value is -(2) - 1 = -3. For the value 10, it is present at index 0 and the method returns 0 directly. The negative result formula ensures that not-found results are always negative, allowing callers to distinguish a not-found response from a valid zero-based index. Searching an unsorted array produces undefined behavior.

Explanation

Java's + operator evaluates left-to-right. In `width + height + " sq units"`, both width and height are int at the first + so arithmetic is performed: 5 + 3 = 8. Then 8 is concatenated with " sq units" to produce "8 sq units". In `"Area: " + width + height`, the first operand is already a String, so "Area: " + 5 produces "Area: 5", and then "Area: 5" + 3 produces "Area: 53". The critical rule is that String concatenation does not trigger for numeric + numeric; arithmetic is performed until at least one operand in a given + sub-expression is a String. Parentheses can force different grouping: `"Area: " + (width + height)` would produce "Area: 8".

Explanation

Java resolves overloaded methods in three sequential phases. Phase one attempts to match using only widening primitive or reference conversions (no boxing). Phase two allows autoboxing and unboxing. Phase three additionally allows varargs. The literal 5 is of type int. No exact match exists because neither method accepts int. In phase one, int widens to double, making process(double d) a valid candidate. Phase two would allow boxing int to Integer to match process(Integer i), but the compiler only advances to phase two if phase one produced no candidates. Because phase one already resolves the call via widening, process(double d) is selected and the output is double. Overload resolution is entirely a compile-time decision; no RuntimeException is involved.