Oracle 1Z0-829 Exam Questions

The code fragment compares four pairs of strings using the equals() and intern() methods. The equals() method compares the content of two strings, while the intern() method returns a canonical representation of a string, which means that it returns a reference to an existing string with the same content in the string pool. The string pool is a memory area where strings are stored and reused to save space and improve performance. The results of the comparisons are as follows:

s1.equals(s2): This returns true because both s1 and s2 have the same content, ''Hello Java 17''.

s1 == s2: This returns false because s1 and s2 are different objects with different references, even though they have the same content. The == operator compares the references of two objects, not their content.

s1.intern() == s2.intern(): This returns true because both s1.intern() and s2.intern() return a reference to the same string object in the string pool, which has the content ''Hello Java 17''. The intern() method ensures that there is only one copy of each distinct string value in the string pool.

''Hello Java 17'' == s2: This returns false because ''Hello Java 17'' is a string literal, which is automatically interned and stored in the string pool, while s2 is a string object created with the new operator, which is not interned by default and stored in the heap. Therefore, they have different references and are not equal using the == operator.

The answer is C because the code fragment uses a different syntax and logic for the reduce operation than the other options. The reduce method in option C takes a single parameter, which is a BinaryOperator that combines two elements of the stream into one. The method returns an Optional, which may or may not contain a value depending on whether the stream is empty or not. The code fragment then adds 5 to the result of the reduce method, regardless of whether it is present or not. This may cause an exception if the Optional is empty, or produce a different value than the other options if the Optional is not empty.

The other options use a different syntax and logic for the reduce operation. They all take two parameters, which are an identity value and a BinaryOperator that combines an element of the stream with an accumulator. The method returns the final accumulator value, which is equal to the identity value if the stream is empty, or the result of applying the BinaryOperator to all elements of the stream otherwise. The code fragments then add 5 to the result of the reduce method, which will always produce a valid value.

For example, suppose listOfNumbers contains [1, 2, 3]. Then, option A will perform the following steps:

Initialize accumulator to identity value 5

Apply BinaryOperator Integer::sum to accumulator and first element: 5 + 1 = 6

Update accumulator to 6

Apply BinaryOperator Integer::sum to accumulator and second element: 6 + 2 = 8

Update accumulator to 8

Apply BinaryOperator Integer::sum to accumulator and third element: 8 + 3 = 11

Update accumulator to 11

Return final accumulator value 11

Add 5 to final accumulator value: 11 + 5 = 16

Option B will perform the same steps as option A, except using a lambda expression instead of a method reference for the BinaryOperator. Option D will perform the same steps as option A, except using parallelStream instead of stream, which may change the order of applying the BinaryOperator but not the final result. Option E will perform the same steps as option A, except using identity value 0 instead of 5.

Option C, however, will perform the following steps:

Apply BinaryOperator Integer::sum to first and second element: 1 + 2 = 3

Apply BinaryOperator Integer::sum to previous result and third element: 3 + 3 = 6

Return Optional containing final result value 6

Add 5 to Optional value: Optional.of(6) + 5 = Optional.of(11)

As you can see, option C produces a different value than the other options, and also uses a different syntax and logic for the reduce operation.Reference:

Oracle Certified Professional: Java SE 17 Developer

Java SE 17 Developer

OCP Oracle Certified Professional Java SE 17 Developer Study Guide

Guide to Stream.reduce()

The code fragment is comparing the values of a, b, and c using the < and > operators. The first comparison, d, is checking if a is less than b and greater than c. Since a is equal to 2, b is equal to -2, and c is equal to -4, this comparison will evaluate to true. The second comparison, e, is checking if a is greater than b and a is greater than c. Since a is equal to 2, b is equal to -2, and c is equal to -4, this comparison will evaluate to false. Therefore, the result will be true 1 false 2.Reference:Operators (The Java Tutorials > Learning the Java Language - Oracle

An automatic module name is derived from the name of the JAR file when it does not contain amodule-info.classfile. If the JAR file has an ''Automatic-Module-Name'' attribute in its main manifest, then its value is the module name. Otherwise, the module name is derived from the JAR file's name by removing any version numbers and converting it to lower case. Therefore, for a JAR nameddisplay-ascii-0.2.jar, the automatic module name would bedisplay-ascii, following these rules.

The code fragment is creating a Duration object with a value of 5000 milliseconds, then printing it. Then, it is creating another Duration object with a value of 60 seconds, then printing it. Finally, it is creating a Period object with a value of 6 days, then printing it. The output will be ''PT5000PT60MP6D''.Reference: https://docs.oracle.com/javase/8/docs/api/java/time/Duration.html, https://docs.oracle.com/javase/8/docs/api/java/time/Period.html