Chapter 3 Core Java APIs

Question 1

API stands for

Answer 1

application programming interface.

Question 2

string is basically a sequence of [Blank]

Answer 2

characters

Question 3

reference types are created using the [Blank] keyword

Answer 3

new

Question 4

3 string concatenation rules:

Answer 4

1. If both operands are numeric, + means numeric addition.
2. If either operand is a String, + means concatenation.
3. The expression is evaluated left to right.

Question 5

System.out.println(1 + 2);
System.out.println(“a” + “b”);
System.out.println(“a” + “b” + 3);
System.out.println(1 + 2 + “c”);

Answer 5

3
ab
ab3
3c

Question 6

int three = 3;
String four = “4”;
System.out.println(1 + 2 + three + four);

Answer 6

1 + 2 = 3
3 + three = 6
6 + four = 64

Question 7

String s = “1”;
s += “2”;
s += 3;
System.out.println(s);

Answer 7

123

Question 8

Can a String be changed when it is created?

Answer 8

No, String is immutable

Question 9

[Blank] means changeable (as in StringBuffers/StringBuilders)

Answer 9

Mutable

Question 10

Immutable classes in Java are [Blank], and subclasses can’t add mutable behavior.

Answer 10

final

Question 11

String s1 = “1”;
String s2 = s1.concat(“2”);
s2.concat(“3”);
System.out.println(s2);

Answer 11

12

Question 12

What location in the JVM collects Strings to reuse and save memory?

Answer 12

String Pool, also known as the intern pool

Question 13

Which one uses the String pool?
String name = "Fluffy";
String name = new String("Fluffy");

Answer 13

First one uses String pool.

Second one creates a new object

Question 14

Java counts from [Blank] when indexed

Answer 14

0

Question 15

String class method: length()

Answer 15

The method length() returns the number of characters in the String. The method signature is as follows:
String string = “animals”;
System.out.println(string.length()); // 7

Question 16

String class method: charAt()

Answer 16

The method charAt() lets you query the string to fi nd out what character is at a specifi c
index. The method signature is as follows:

String string = “animals”;
System.out.println(string.charAt(0)); // a
System.out.println(string.charAt(6)); // s
System.out.println(string.charAt(7)); // throws exception

Question 17

String class method: indexOf()

Answer 17

The method indexOf()looks at the characters in the string and finds the first index that matches the desired value. indexOf can work with an individual character or a whole String as input. It can also start from a requested position. The method signatures are as follows:

int indexOf(char ch)
int indexOf(char ch, index fromIndex)
int indexOf(String str)
int indexOf(String str, index fromIndex)

String string = “animals”;
System.out.println(string.indexOf(‘a’)); // 0
System.out.println(string.indexOf(“al”)); // 4
System.out.println(string.indexOf(‘a’, 4)); // 4
System.out.println(string.indexOf(“al”, 5)); // -1

Question 18

String class method: substring()

Answer 18

The method substring() also looks for characters in a string. It returns parts of the string.
The fi rst parameter is the index to start with for the returned string. As usual, this is a
zero-based index. There is an optional second parameter, which is the end index you want
to stop at.
Notice we said “stop at” rather than “include.” This means the endIndex parameter is
allowed to be 1 past the end of the sequence if you want to stop at the end of the sequence.
That would be redundant, though, since you could omit the second parameter entirely in
that case. In your own code, you want to avoid this redundancy. Don’t be surprised if the
exam uses it though. The method signatures are as follows:
int substring(int beginIndex)
int substring(int beginIndex, int endIndex)
String string = “animals”;
System.out.println(string.substring(3)); // mals
System.out.println(string.substring(string.indexOf(‘m’))); // mals
System.out.println(string.substring(3, 4)); // m
System.out.println(string.substring(3, 7)); // mals

Question 19

String class method: toLowerCase() and toUpperCase()
String string = "animals";
System.out.println(string.toUpperCase()); 
System.out.println("Abc123".toLowerCase());

Answer 19

ANIMALS

abc123

Question 20

String class method: equals() and equalsIgnoreCase()
System.out.println("abc".equals("ABC")); 
System.out.println("ABC".equals("ABC")); 
System.out.println("abc".equalsIgnoreCase("ABC"));

Answer 20

false
true
true

Question 21

String class method: startsWith() and endsWith()
System.out.println("abc".startsWith("a"));
System.out.println("abc".startsWith("A"));
System.out.println("abc".endsWith("c")); 
System.out.println("abc".endsWith("a"));

Answer 21

true
false
true
false

Question 22

String class method: contains()
System.out.println("abc".contains("b")); // true
System.out.println("abc".contains("B")); // false

Answer 22

true

false