Introduction
Converting a string to an integer on Android uses standard Java/Kotlin methods since Android runs on the JVM. The primary methods are Integer.parseInt() (returns a primitive int) and Integer.valueOf() (returns an Integer object). Both throw NumberFormatException if the string is not a valid integer, so you must handle this exception when parsing user input from EditText, intent extras, or API responses. In Kotlin, use toIntOrNull() for a null-safe conversion that avoids try/catch blocks entirely.
Java: Integer.parseInt()
1// Basic conversion
2String numberStr = "42";
3int number = Integer.parseInt(numberStr);
4System.out.println(number); // 42
5
6// From EditText
7EditText editText = findViewById(R.id.editTextNumber);
8String input = editText.getText().toString().trim();
9int value = Integer.parseInt(input);
10
11// With radix (base)
12int hex = Integer.parseInt("FF", 16); // 255
13int binary = Integer.parseInt("1010", 2); // 10
14int octal = Integer.parseInt("17", 8); // 15
1public int parseIntSafe(String str, int defaultValue) {
2 try {
3 return Integer.parseInt(str.trim());
4 } catch (NumberFormatException e) {
5 return defaultValue;
6 }
7}
8
9// Usage
10int age = parseIntSafe(editText.getText().toString(), 0);
11int quantity = parseIntSafe("not a number", -1); // Returns -1
12int count = parseIntSafe("", 0); // Returns 0
13int valid = parseIntSafe("123", 0); // Returns 123
Java: Integer.valueOf()
1// Returns Integer object (boxed)
2Integer boxed = Integer.valueOf("42");
3
4// Auto-unboxing to int
5int number = Integer.valueOf("42");
6
7// Difference from parseInt:
8// parseInt returns primitive int
9// valueOf returns cached Integer object (caches -128 to 127)
10Integer a = Integer.valueOf("100");
11Integer b = Integer.valueOf("100");
12System.out.println(a == b); // true (cached)
13
14Integer c = Integer.valueOf("200");
15Integer d = Integer.valueOf("200");
16System.out.println(c == d); // false (not cached, use .equals())
Kotlin: toInt() and toIntOrNull()
1// Direct conversion (throws NumberFormatException)
2val number: Int = "42".toInt()
3
4// Null-safe conversion (returns null on failure)
5val safe: Int? = "42".toIntOrNull() // 42
6val invalid: Int? = "abc".toIntOrNull() // null
7val empty: Int? = "".toIntOrNull() // null
8val overflow: Int? = "99999999999".toIntOrNull() // null (exceeds Int range)
9
10// With default value using Elvis operator
11val age: Int = editText.text.toString().toIntOrNull() ?: 0
12val quantity: Int = "not a number".toIntOrNull() ?: -1
13
14// With radix
15val hex: Int = "FF".toInt(16) // 255
16val hexSafe: Int? = "GG".toIntOrNull(16) // null (invalid hex)
Common Android Use Cases
From EditText
1// Kotlin
2val editText: EditText = findViewById(R.id.editTextAge)
3val ageStr = editText.text.toString().trim()
4val age = ageStr.toIntOrNull()
5
6if (age == null || age < 0 || age > 150) {
7 editText.error = "Please enter a valid age"
8} else {
9 processAge(age)
10}
1// Java
2EditText editText = findViewById(R.id.editTextAge);
3String ageStr = editText.getText().toString().trim();
4
5try {
6 int age = Integer.parseInt(ageStr);
7 if (age < 0 || age > 150) {
8 editText.setError("Age must be between 0 and 150");
9 } else {
10 processAge(age);
11 }
12} catch (NumberFormatException e) {
13 editText.setError("Please enter a valid number");
14}
1// Sending
2val intent = Intent(this, DetailActivity::class.java)
3intent.putExtra("item_id", 42) // Send as int directly
4intent.putExtra("item_id_str", "42") // Or as string
5
6// Receiving
7val id = intent.getIntExtra("item_id", -1) // Returns int directly
8val idStr = intent.getStringExtra("item_id_str")
9val idParsed = idStr?.toIntOrNull() ?: -1
From SharedPreferences
1val prefs = getSharedPreferences("settings", MODE_PRIVATE)
2
3// Store as int
4prefs.edit().putInt("count", 42).apply()
5val count = prefs.getInt("count", 0)
6
7// Store as string (from older code)
8prefs.edit().putString("count", "42").apply()
9val countStr = prefs.getString("count", "0")
10val countParsed = countStr?.toIntOrNull() ?: 0
From JSON/API Responses
1import org.json.JSONObject
2
3val json = JSONObject("""{"id": "123", "count": 42}""")
4
5// String field that should be int
6val id = json.getString("id").toIntOrNull() ?: 0
7
8// Int field (already an int in JSON)
9val count = json.getInt("count")
10
11// Optional field
12val optionalCount = if (json.has("views")) json.getInt("views") else 0
Other Numeric Conversions
1// Long
2val longVal: Long = "9999999999".toLongOrNull() ?: 0L
3
4// Double
5val doubleVal: Double = "3.14".toDoubleOrNull() ?: 0.0
6
7// Float
8val floatVal: Float = "2.5".toFloatOrNull() ?: 0f
9
10// Java equivalents
11long l = Long.parseLong("9999999999");
12double d = Double.parseDouble("3.14");
13float f = Float.parseFloat("2.5");
Common Pitfalls
Not trimming whitespace before parsing: Integer.parseInt(" 42 ") throws NumberFormatException because of leading/trailing spaces. Always call .trim() on the string before parsing, especially when reading from EditText.
Forgetting to handle NumberFormatException: User input is unpredictable. Parsing without try/catch or toIntOrNull() crashes the app when the user enters non-numeric text. Always validate or catch exceptions on user-provided strings.
Comparing Integer.valueOf() results with ==: Integer.valueOf() caches values from -128 to 127. Beyond that range, == compares object references and returns false even for equal values. Use .equals() for Integer object comparison.
Parsing strings with decimal points as integers: Integer.parseInt("3.14") throws NumberFormatException. To handle decimals, parse as Double.parseDouble() first, then cast to int if truncation is acceptable: (int) Double.parseDouble("3.14").
Not setting inputType="number" on EditText: Without android:inputType="number" in XML, the soft keyboard shows letters, making non-numeric input easy. Setting the input type restricts the keyboard to digits, reducing (but not eliminating) the need for parsing validation.
Summary
Use Integer.parseInt() in Java or .toInt() in Kotlin for basic string-to-integer conversion
Use .toIntOrNull() in Kotlin for null-safe parsing that avoids try/catch blocks
Always handle NumberFormatException when parsing user input or external data
Trim whitespace before parsing and set inputType="number" on EditText to reduce invalid input
For intent extras and SharedPreferences, prefer storing integers directly (putInt) instead of converting from strings
