🔍 Java How-To Examples – Practical Snippets with Explanations (2025 Edition)

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🧲 Introduction – Learn Java by Doing

In Java, practicing small problem-solving examples helps build a strong foundation. This guide provides simple, practical code examples that cover basic operations, string manipulations, array processing, loops, conditionals, and working with data structures.

🎯 In this guide, you’ll learn:

• How to solve common coding tasks using Java
• Understand how each snippet works step-by-step
• Strengthen your fundamentals with hands-on code

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📌 Topics Covered with Explanations

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➕ 1. Add Two Numbers

💡 Explanation: Adding two integers using the + operator.

int a = 10, b = 20;
int sum = a + b;
System.out.println("Sum = " + sum);

🔍 Code Explanation:

• a and b are declared and initialized.
• Their sum is stored in sum.
• The result is printed using System.out.println().

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✍️ 2. Count Words in a String

💡 Explanation: Count the number of words in a string using .split() method.

String text = "Java is powerful";
int wordCount = text.split("\\s+").length;
System.out.println("Words: " + wordCount);

🔍 Code Explanation:

• split("\\s+") splits the string on whitespace.
• .length gives the total number of words.

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🔁 3. Reverse a String

💡 Explanation: Reversing characters using StringBuilder.

String str = "Java";
String reversed = new StringBuilder(str).reverse().toString();
System.out.println(reversed);

🔍 Code Explanation:

• StringBuilder is used for mutable strings.
• reverse() reverses the characters.
• toString() converts it back to a string.

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➗ 4. Sum of Array Elements

💡 Explanation: Iterate through an array and add all elements.

int[] numbers = {10, 20, 30};
int sum = 0;
for (int num : numbers) {
  sum += num;
}
System.out.println("Sum = " + sum);

🔍 Code Explanation:

• A for-each loop adds each element to sum.
• The total is printed after the loop.

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🔄 5. Convert String to Array

💡 Explanation: Convert a comma-separated string to an array.

String str = "Java,Python,C++";
String[] langs = str.split(",");
System.out.println(Arrays.toString(langs));

🔍 Code Explanation:

• .split(",") splits the string into an array.
• Arrays.toString() displays the array content.

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📊 6. Sort an Array

💡 Explanation: Sorting an integer array in ascending order.

int[] arr = {5, 2, 8, 1};
Arrays.sort(arr);
System.out.println(Arrays.toString(arr));

🔍 Code Explanation:

• Arrays.sort() performs in-place sorting.
• The sorted array is printed.

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🧮 7. Find Array Average

💡 Explanation: Calculate the average of array elements.

int[] values = {10, 20, 30};
int sum = 0;
for (int v : values) sum += v;
double avg = (double) sum / values.length;
System.out.println("Average = " + avg);

🔍 Code Explanation:

• Total sum is divided by the number of elements using .length.
• Casting ensures correct decimal result.

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🔍 8. Find Smallest Element

💡 Explanation: Find the minimum value in an array.

int[] nums = {4, 7, 1, 9};
int min = nums[0];
for (int n : nums) {
  if (n < min) min = n;
}
System.out.println("Min = " + min);

🔍 Code Explanation:

• Assume the first value as smallest.
• Update min if a smaller value is found during loop.

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🔁 9. Loop Through ArrayList

💡 Explanation: Looping over an ArrayList using for-each loop.

ArrayList<String> list = new ArrayList<>(List.of("Java", "Python", "C"));
for (String lang : list) {
  System.out.println(lang);
}

🔍 Code Explanation:

• List.of() initializes the list.
• The loop prints each element.

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🔁 10. Loop Through HashMap

💡 Explanation: Access keys and values in a HashMap.

HashMap<String, Integer> map = new HashMap<>();
map.put("A", 1);
map.put("B", 2);

for (Map.Entry<String, Integer> entry : map.entrySet()) {
  System.out.println(entry.getKey() + ": " + entry.getValue());
}

🔍 Code Explanation:

• entrySet() returns key-value pairs.
• Each entry is printed.

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🎯 11. Loop Through Enum

💡 Explanation: Use .values() to loop through enum constants.

enum Days { MON, TUE, WED }

for (Days d : Days.values()) {
  System.out.println(d);
}

🔍 Code Explanation:

• .values() returns all constants.
• Loop prints each day.

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📐 12. Area of Rectangle

💡 Explanation: Calculate area using formula length * width.

int length = 5, width = 3;
int area = length * width;
System.out.println("Area = " + area);

🔍 Code Explanation:

• Variables hold dimensions.
• Result is computed and printed.

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🔢 13. Even or Odd Number

💡 Explanation: Use modulus operator to check parity.

int num = 6;
System.out.println(num % 2 == 0 ? "Even" : "Odd");

🔍 Code Explanation:

• % 2 == 0 checks if number is divisible by 2.

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➕ 14. Positive or Negative Number

💡 Explanation: Check sign of number using conditional blocks.

int number = -5;
if (number > 0)
  System.out.println("Positive");
else if (number < 0)
  System.out.println("Negative");
else
  System.out.println("Zero");

🔍 Code Explanation:

• Conditions identify sign status of the number.

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📏 15. Square Root of a Number

💡 Explanation: Use Math.sqrt() to calculate square root.

double n = 16;
double sqrt = Math.sqrt(n);
System.out.println("Square root = " + sqrt);

🔍 Code Explanation:

• Math.sqrt() returns square root as a double.

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🎲 16. Generate Random Number

💡 Explanation: Use Math.random() to get a value between 0 and 100.

int rand = (int)(Math.random() * 100);
System.out.println("Random: " + rand);

🔍 Code Explanation:

• Math.random() gives value [0.0, 1.0)
• Multiply and cast to get an integer range.

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📌 Summary – Recap & Next Steps

These how-to examples are your quick reference guide for writing effective Java code.

🔍 Key Takeaways:

• Learn core Java operations through real-world snippets
• Practice string, array, and math problems
• Loop through collections and enums
• Understand conditionals and conversions

⚙️ Next Steps:

• Try modifying these examples to accept user input
• Combine multiple examples into a mini-project
• Explore more how-to tasks like file reading, regex, and recursion

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❓ Frequently Asked Questions (FAQs)

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❓ Can these examples be used in coding interviews?
✅ Yes, they demonstrate common logic and help you explain your thinking clearly.

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❓ How can I take input instead of hardcoding values?
✅ Use Scanner for user input. Example: Scanner sc = new Scanner(System.in);

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❓ Are these examples valid for Java 17 and newer?
✅ Yes. All code is compatible with Java 8 and above.

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❓ Can I use these examples for Android development?
✅ Yes. Logic remains the same, but output goes to UI components instead of console.

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❓ Where can I practice these online?
✅ Try platforms like Replit, JDoodle, or use an IDE like IntelliJ/Eclipse.

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