chapter 1_JavaBuildingBlocks

Question 1

1. What are the primary elements in Java Class?

Answer 1

a. methods (functions)

b. fields, (variables)

Question 2

2. what are the 3 types of comments?

Answer 2

a. A single-line comment -> //
b. A multiple-line comment
- > /* Multiple
* line comment
* /
c. Javadoc comment
- > * Javadoc multiple-line comment
* @author Jeanne and Scott
* /

Question 3

3. what command need to run java

Answer 3

• javac .java

- java

Question 4

4. what java not import

Answer 4

• It doesn’t import child packages, fi elds, or methods; it imports only classes.

Question 5

5. what is special package that java automatically import

Answer 5

• java.lang.

Question 6

6. how many import that redundant?

1: import java.lang.System;
2: import java.lang.;
3: import java.util.Random;
4: import java.util.;
5: public class ImportExample {
6: public static void main(String[] args) {
7: Random r = new Random();
8: System.out.println(r.nextInt(10));
9: }
10: }

Answer 6

• three of the imports are redundant. Lines 1 and 2 are redundant because everything in java, Line 4 is also redundant in this example because Random is already imported from java.util.Random.

Question 7

7. What is constructor look like? can you give some example?

Answer 7

public class Chick {
public Chick() {
System.out.println("in constructor");
}
}

Question 8

8. What is instance look like? can you give some example?

Answer 8

Random r = new Random();

Question 9

9. what is read and write variables is known as?

Answer 9

Reading a variable is known as getting it. Writing to a variable is known as setting it.

Question 10

10. What is ‘instace initializers’?

Answer 10

Code blocks that appear outside a method.

Question 11

11. Explain order of initialization

Answer 11

• Fields and instance initializer blocks are run in the order in which they appear in
  the file.
• The constructor runs after all fields and instance initializer blocks have run.

Question 12

12. how many built-in data types or Java primitive types, and state it.

Answer 12

Eight, which are boolean, byte, short, int, long, float, double and char

Question 13

13. Can you state all keyword and type contains in Java primitive type

Answer 13

a. boolean - true or false
b. byte - 8-bit integral value
c. short - 16-bit integral value
d. int - 32-bit integral value
e. long - 64-bit integral value
f. float - 32-bit floating-point value
g. double - 64-bit floating-point value
h. char - 16-bit Unicode value

Question 14

14. how many base can write in java, and how to write it

Answer 14

a. base 10 - System.out.println(56); // 56
b. binary - System.out.println(0b11); // 3
c. octal - System.out.println(017); // 15
d. hexadecimal - System.out.println(0x1F); // 31

Question 15

15. explain about numeric literals

Answer 15

can have underscores in numbers to make them easier to read, You can add
underscores anywhere except at the beginning of a literal, the end of a literal, right before a
decimal point, or right after a decimal point.

Question 16

16. How many ways value can be assigned to reference?

Answer 16

Two

a. A reference can be assigned to another object of the same type.
b. A reference can be assigned to a new object using the new keyword.

Question 17

17. state few key difference between primitives and reference type.

Answer 17

a. Reference types can assigned to null, while primitive will give compiler error if assigned to null.
b. Reference types can used to call method when not point to null. While primitives do not have method.
c. all the primitive types have lowercase type names

Question 18

18. Fiure out which of the following are legal declarations.
boolean b1, b2;
String s1 = "1", s2;
double d1, double d2;
int i1; int i2;
int i3; i4;

Answer 18

• The fi rst statement is legal. It declares two variables without initializing them.
• The second statement is also legal. It declares two variables and initializes only one of them.
• The third statement is not legal. Java does not allow you to declare two different types in the same statement.
• The fourth statement is legal. Although int does appear twice, each one is in a separate statement.
• The fi fth statement is not legal. Again, we have two completely different statements on the same line. The second one is not a valid declaration because it omits the type.

Question 19

19. What is rules about identifier names.

Answer 19

a. The name must begin with a letter or the symbol $ or _.
b. Subsequent characters may also be numbers.
c. cannot use the same name as a Java reserved word, but you can use versions of the keywords that only differ in case.

Question 20

20. can you explain about local variables.

Answer 20

a. A local variable is a variable defi ned within a method.
b. Local variables must be initialized before use.
c. They do not have a default value and contain garbage data until initialized.
d. The compiler will not let you read an uninitialized value.

Question 21

21. explain about Instance and Class variable.

Answer 21

a. variables that are not local variables
b. Class variables are shared across multiple objects. We can tell its as class variable because it has static keyword
c. not require to declare, it will give default value

Question 22

22. state the Default initialization value by type.

Answer 22

Variable type - Default initialization value

a. boolean - false
b. byte, short, int, long - 0 (in the type’s bit-length)
c. float, double - 0.0 (in the type’s bit-length)
d. char - ‘\u0000’ (NUL)
e. All object references (everything else) - null

Question 23

23. state the rules on variables scope.

Answer 23

a. Local variables—in scope from declaration to end of block
b. Instance variables—in scope from declaration until object garbage collected
c. Class variables—in scope from declaration until program ends

Question 24

24. whats the functions of garbage collector?

Answer 24

process of automatically freeing memory on the heap by deleting objects that are no longer reachable in your program.

Question 25

25. Where Java Object are stored?

Answer 25

All Java objects are stored in your program memory’s heap.

Question 26

26. Can you explained about Heap?

Answer 26

• also referred as free store, represented large pool of unused memory allocated to your Java application
• may be quite large, but its limit to size, depend on environment
• will run out of memory, if program keeps initiating object and leave them on heap.

Question 27

27. what is System.gc() is used for?

Answer 27

might be a good time for Java to kick off a garbage collection run. Java is free to ignore the request.

Question 28

28. What situation is the object no longer reachable?

Answer 28

■ The object no longer has any references pointing to it.

■ All references to the object have gone out of scope.

Question 29

29. figure out when each object fi rst becomes eligible for garbage collection:
    1: public class Scope {
    2: public static void main(String[] args) {
    3: String one, two;
    4: one = new String(“a”);
    5: two = new String(“b”);
    6: one = two;
    7: String three = one;
    8: one = null;
    9: } }

Answer 29

a. Draw a box with the string “a” in it and draw an arrow from the word one to that box. Line 5 is similar. Draw another box with the string “b” in it this time and an arrow from the word two
b. On line 6, the variable one changes to point to “b”. Either erase or cross out the arrow from one and draw a new arrow from one to “b”. On line 7, we have a new variable, so write the word three and draw an arrow from three to “b”.

c. Finally, cross out the line between one and “b” since line 8 sets this variable to null.
d. On line 6, we got rid of the only arrow pointing to “a”, making that object eligible for garbage collection.

e. “b” has arrows pointing to it until it goes out of scope. This means “b” doesn’t go out of scope until the end of the method on line 9.

Question 30

30. can u explained to me about finalize()

Answer 30

• This method gets called if the garbage collector tries to collect the object.
• If the garbage collector fails to collect the object and tries to run it again later, the method doesn’t get called a second time.