Topic 9.2: Working with Selected classes from the Java API - Create and manipulate Strings

Question 1

What is string interning and how does it optimize memory usage?

Answer 1

This is the process of storing string literals in a string pool to optimize memory usage.

When encountering a string literal, the JVM checks if it already exists in the pool. If it does, a reference to the existing string is returned. If not, a new string object is created and added to the pool.

This ensures that only one copy of each unique string exists in memory, reducing memory footprint and enhancing performance.

Question 2

The equalsIgnoreCase() method can be used for this

Answer 2

What method can be used for case-insensitive string comparison in Java?

Question 3

To achieve this you can use the substring() method

String text = "Hello, World!";
String substring = text.substring(7);

Answer 3

How can you extract a substring from a string in Java?

Question 4

To achieve this, you can use the startsWith() method.

String text = "Hello, World!";
boolean startsWithHello = text.startsWith("Hello");

Answer 4

How can you check if a string starts with a specific prefix?

Question 5

To achieve this you can use the toUpperCase() method

String text = "Hello, World!";
String uppercase = text.toUpperCase();

Answer 5

How can you convert a string to uppercase in Java?

Question 6

How can you convert a string to uppercase in Java?

Answer 6

To achieve this you can use the toUpperCase() method

String text = "Hello, World!";
String uppercase = text.toUpperCase();

Question 7

How can you create strings in Java using string literals or the new keyword?

Answer 7

String literals involve enclosing characters within double quotation marks, such as “Hello, world!”. The new keyword can be used with the String class constructor, as in new String(“John”).

Question 8

To achieve this you can use the trim() method

String text = "   Hello, World!   ";
String trimmed = text.trim();

Answer 8

How can you remove leading and trailing whitespace from a string in Java?

Question 9

How can you check if a string starts with a specific prefix?

Answer 9

To achieve this, you can use the startsWith() method.

String text = "Hello, World!";
boolean startsWithHello = text.startsWith("Hello");

Question 10

How can you search for the first occurrence of a substring within a string in Java?

Answer 10

To achieve this you can use the indexOf() method, which takes the substring as a parameter and returns the index of the first occurrence. If the substring is not found, it returns -1.

For example, given the string “Hello, World!”, calling indexOf(“o”) would return 4.

String text = "Hello, World!";
int index1 = text.indexOf("o");
int index2 = text.indexOf("XYZ");

Question 11

To achieve this you can use the replace() method with a single character as the target and the replacement value

For example, given the string “Hello, World!”, calling replace(‘o’, ‘e’) would return “Helle, Werld!”.

String text = "Hello, World!";
String replaced = text.replace('o', 'e');

Answer 11

How can you replace a character within a string in Java?

Question 12

How can you find the index of the last occurrence of a specific substring within a string?

Answer 12

To achieve this, you can use the lastIndexOf() method.

String text = "Hello, World!";
int lastIndex = text.lastIndexOf("o");

Question 13

Behaviour of this:

The replacement proceeds from the beginning of the string to the end. For example, replacing “aa” with “b” in the string “aaa” will result in “ba” rather than “ab”.

Answer 13

What is the behavior of the replace() method in Java?

Question 14

To acheive this you can use the split() method, which takes a delimiter as a parameter and returns an array of strings.

For example, given the string “Hello, World!”, calling split(“, “) would return an array containing [“Hello”, “World!”].

String text = "Hello, World!";
String[] words = text.split(", ");

Answer 14

How can you split a string into an array of substrings in Java?

Question 15

How can you extract a substring from a string in Java?

Answer 15

To achieve this you can use the substring() method

String text = "Hello, World!";
String substring = text.substring(7);

Question 16

How can you convert other data types to strings?

Answer 16

This can be achieved using the valueOf() or toString() methods.

For example, String.valueOf(10) or Integer.toString(5).

Question 17

How can you remove leading and trailing whitespace from a string in Java?

Answer 17

To achieve this you can use the trim() method

String text = "   Hello, World!   ";
String trimmed = text.trim();

Question 18

To achieve this you can use the indexOf() method, which takes the substring as a parameter and returns the index of the first occurrence. If the substring is not found, it returns -1.

For example, given the string “Hello, World!”, calling indexOf(“o”) would return 4.

String text = "Hello, World!";
int index1 = text.indexOf("o");
int index2 = text.indexOf("XYZ");

Answer 18

How can you search for the first occurrence of a substring within a string in Java?

Question 19

To achieve this, you can use the endsWith() method.

String text = "Hello, World!";
boolean endsWithWorld = text.endsWith("World!");

Answer 19

How can you check if a string ends with a specific suffix?

Question 20

String literals involve enclosing characters within double quotation marks, such as “Hello, world!”. The new keyword can be used with the String class constructor, as in new String(“John”).

Answer 20

How can you create strings in Java using string literals or the new keyword?

Question 21

To achieve this you can use the toLowerCase() method

String text = "Hello, World!";
String lowercase = text.toLowerCase();

Answer 21

How can you convert a string to lowercase in Java?

Question 22

This can be acieved using methods like parseInt(), parseDouble(), etc.

For example, Integer.parseInt("10") or Double.parseDouble("3.14").

Answer 22

How can you parse strings into other data types?

Question 23

How can you parse strings into other data types?

Answer 23

This can be acieved using methods like parseInt(), parseDouble(), etc.

For example, Integer.parseInt("10") or Double.parseDouble("3.14").

Question 24

The format() method can be used to format strings based on patterns.

String name = "Alice";
int age = 25;
String formatted = String.format("My name is %s and I am %d years old.", name, age);

Answer 24

What method can be used to format strings based on patterns?

Question 25

How can you split a string into an array of substrings in Java?

Answer 25

To acheive this you can use the split() method, which takes a delimiter as a parameter and returns an array of strings.

For example, given the string “Hello, World!”, calling split(“, “) would return an array containing [“Hello”, “World!”].

String text = "Hello, World!";
String[] words = text.split(", ");

Question 26

How can you replace substrings within a string in Java?

Answer 26

To achieve this you can use the replace() method with a substring as the target and the replacement value.

For example, given the string “Hello, World!”, calling replace(“Hello”, “Hi”) would return “Hi, World!”.

String text = "Hello, World!";
String replaced = text.replace("Hello", "Hi");

Question 27

How can you convert a string to lowercase in Java?

Answer 27

To achieve this you can use the toLowerCase() method

String text = "Hello, World!";
String lowercase = text.toLowerCase();

Question 28

To achieve this you can use the replace() method with a substring as the target and the replacement value.

For example, given the string “Hello, World!”, calling replace(“Hello”, “Hi”) would return “Hi, World!”.

String text = "Hello, World!";
String replaced = text.replace("Hello", "Hi");

Answer 28

How can you replace substrings within a string in Java?

Question 29

What method can be used to format strings based on patterns?

Answer 29

The format() method can be used to format strings based on patterns.

String name = "Alice";
int age = 25;
String formatted = String.format("My name is %s and I am %d years old.", name, age);

Question 30

What is the behavior of the replace() method in Java?

Answer 30

Behaviour of this:

The replacement proceeds from the beginning of the string to the end. For example, replacing “aa” with “b” in the string “aaa” will result in “ba” rather than “ab”.

Question 31

This is the process of storing string literals in a string pool to optimize memory usage.

When encountering a string literal, the JVM checks if it already exists in the pool. If it does, a reference to the existing string is returned. If not, a new string object is created and added to the pool.

This ensures that only one copy of each unique string exists in memory, reducing memory footprint and enhancing performance.

Answer 31

What is string interning and how does it optimize memory usage?

Question 32

This can be achieved using the valueOf() or toString() methods.

For example, String.valueOf(10) or Integer.toString(5).

Answer 32

How can you convert other data types to strings?

Question 33

How can you check if a string ends with a specific suffix?

Answer 33

To achieve this, you can use the endsWith() method.

String text = "Hello, World!";
boolean endsWithWorld = text.endsWith("World!");

Question 34

How can you replace a character within a string in Java?

Answer 34

To achieve this you can use the replace() method with a single character as the target and the replacement value

For example, given the string “Hello, World!”, calling replace(‘o’, ‘e’) would return “Helle, Werld!”.

String text = "Hello, World!";
String replaced = text.replace('o', 'e');

Question 35

What method can be used for case-insensitive string comparison in Java?

Answer 35

The equalsIgnoreCase() method can be used for this

Question 36

To achieve this, you can use the lastIndexOf() method.

String text = "Hello, World!";
int lastIndex = text.lastIndexOf("o");

Answer 36

How can you find the index of the last occurrence of a specific substring within a string?