Why strings are special in Java - Challenge Your Understanding

trophy

Challenge - 5 Problems

💻 code output

intermediate

What is the output of this Java code involving String comparison?

Consider the following Java code snippet:

public class Test {
    public static void main(String[] args) {
        String a = "hello";
        String b = "hello";
        String c = new String("hello");
        System.out.println(a == b);
        System.out.println(a == c);
    }
}

What will be the output when this code runs?

Java

public class Test {
    public static void main(String[] args) {
        String a = "hello";
        String b = "hello";
        String c = new String("hello");
        System.out.println(a == b);
        System.out.println(a == c);
    }
}

A

false
false

B

true
false

C

true
true

D

false
true

🧠 conceptual

intermediate

Why are String objects immutable in Java?

Why did Java designers make String objects immutable?

A To allow strings to be safely shared and reused without changes

B To make strings faster to modify in place

C To prevent strings from being used as keys in collections

D To allow strings to be garbage collected immediately after use

💻 code output

advanced

What is the output of this code using StringBuilder and String?

Examine this Java code:

public class Test {
    public static void main(String[] args) {
        String s = "abc";
        StringBuilder sb = new StringBuilder(s);
        sb.append("def");
        System.out.println(s);
        System.out.println(sb.toString());
    }
}

What will be printed?

Java

public class Test {
    public static void main(String[] args) {
        String s = "abc";
        StringBuilder sb = new StringBuilder(s);
        sb.append("def");
        System.out.println(s);
        System.out.println(sb.toString());
    }
}

A

abc
abcdef

B

abcdef
abcdef

C

abc
abc

D

abcdef
abc

🔧 debug

advanced

What error does this code cause?

Look at this Java code snippet:

public class Test {
    public static void main(String[] args) {
        String s = null;
        if (s.equals("test")) {
            System.out.println("Match");
        } else {
            System.out.println("No match");
        }
    }
}

What happens when you run this code?

Java

public class Test {
    public static void main(String[] args) {
        String s = null;
        if (s.equals("test")) {
            System.out.println("Match");
        } else {
            System.out.println("No match");
        }
    }
}

A Prints "Match"

B Prints "No match"

C NullPointerException

D Compilation error

🚀 application

expert

How many unique strings are in this array after interning?

Consider this Java code:

public class Test {
    public static void main(String[] args) {
        String[] arr = new String[] {"cat", new String("cat"), "dog", new String("dog")};
        for (int i = 0; i < arr.length; i++) {
            arr[i] = arr[i].intern();
        }
        java.util.Set set = new java.util.HashSet<>();
        for (String s : arr) {
            set.add(s);
        }
        System.out.println(set.size());
    }
}

What number will be printed?

Java

public class Test {
    public static void main(String[] args) {
        String[] arr = new String[] {"cat", new String("cat"), "dog", new String("dog")};
        for (int i = 0; i < arr.length; i++) {
            arr[i] = arr[i].intern();
        }
        java.util.Set<String> set = new java.util.HashSet<>();
        for (String s : arr) {
            set.add(s);
        }
        System.out.println(set.size());
    }
}

A 1

B 4

C 3

D 2