Strings.md

Java String Questions and Answers

1. How is a String object created in Java?

Answer:

• A String object can be created in two primary ways:
  1. Using string literals:

     String str = "Hello";

     • Stored in the String pool, a special memory area in the JVM for strings, for memory optimization.
  2. Using the new keyword:

     String str = new String("Hello");

     • Creates a new String object in the heap memory, even if the same string exists in the pool.
     • Avoid unless explicitly needed to create a distinct object.

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2. What is the difference between String and CharSequence?

Answer:

• CharSequence is an interface representing a sequence of characters, while String is a concrete implementation of CharSequence.
• Key differences:
  • CharSequence is a general-purpose API for various string-like objects (e.g., String, StringBuilder, StringBuffer).
  • String is immutable and provides additional methods for manipulating and comparing strings.

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3. Explain the purpose of the String.intern() method.

Answer:

• The intern() method ensures that a string is stored in the String pool.
• If the string already exists in the pool, it returns the reference; otherwise, it adds the string to the pool.
• This helps in saving memory by avoiding duplicate string objects.

Example:

String s1 = new String("Java").intern();
String s2 = "Java";
System.out.println(s1 == s2); // true

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4. What is the use of the split() method in the String class?

Answer:

• The split() method splits a string into an array of substrings using a specified delimiter (regular expression).

Example:

String str = "apple,banana,grape";
String[] fruits = str.split(",");
for (String fruit : fruits) {
    System.out.println(fruit);
}

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5. How can you reverse a String in Java without using a library?

Answer:

• Reversing a string manually involves iterating over its characters in reverse order and building the reversed string.

Example:

public class ReverseString {
    public static String reverse(String str) {
        StringBuilder reversed = new StringBuilder();
        for (int i = str.length() - 1; i >= 0; i--) {
            reversed.append(str.charAt(i));
        }
        return reversed.toString();
    }
}

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6. How can you check if a String is a palindrome?

Answer:

• A palindrome reads the same backward as forward. This can be checked by comparing characters from the beginning and end of the string.

Example:

public class PalindromeChecker {
    public static boolean isPalindrome(String str) {
        int left = 0, right = str.length() - 1;
        while (left < right) {
            if (str.charAt(left) != str.charAt(right)) {
                return false;
            }
            left++;
            right--;
        }
        return true;
    }
}

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7. Explain how String.format() works.

Answer:

• String.format() allows for dynamic construction of formatted strings using placeholders like %s (string), %d (integer), %f (float), etc.

Example:

String name = "John";
int score = 85;
String formatted = String.format("Hello %s, you scored %d marks!", name, score);
System.out.println(formatted);

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8. How does the String.join() method work?

Answer:

• The join() method concatenates multiple strings with a specified delimiter in between.

Example:

String result = String.join(", ", "apple", "banana", "grape");
System.out.println(result); // Output: apple, banana, grape

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9. What are escape sequences in strings? Provide examples.

Answer:

• Escape sequences are special characters prefixed with a backslash (\) that represent certain actions or characters.
  • Examples:
    • \n: Newline
    • \t: Tab
    • \\: Backslash
    • \": Double quote

Example:

String str = "Hello\nWorld";
System.out.println(str);

Output:

Hello
World

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10. Compare the efficiency of String concatenation using + operator and StringBuilder.

Answer:

• + operator:

  • Creates new string objects for each concatenation, leading to higher memory usage.
  • Inefficient for repetitive concatenation in loops.

• StringBuilder:

  • Uses a mutable buffer, reducing memory overhead.
  • Best choice for multiple or repetitive string manipulations.

Example:

StringBuilder sb = new StringBuilder("Hello");
sb.append(" World");
System.out.println(sb.toString());