Java
Overview
Java is a widely-used enterprise programming language. Runner Codes provides OpenJDK 17 for executing Java code with automatic compilation.
Specifications
| Property | Value |
|---|---|
| Base OS | Debian Bookworm |
| Version | OpenJDK 17 |
| Rootfs Size | 600 MB |
| Execution | Compiled (javac + java) |
| File Extension | .java |
| Compile Command | javac Main.java |
| Run Command | java Main |
| Execution Time | ~752ms |
1. Create Rootfs with infra.operator
sudo infra.operator rootfs create --name java --size 600 --base debian --packages "openjdk-17-jdk-headless"
2. Create Snapshot
sudo infra.operator snapshot create --lang java --mem 512 --vcpus 1
3. Upload rootfs to S3
sudo infra.operator rootfs upload --lang java --bucket runner-codes
3. Upload snapshot to S3
sudo infra.operator snapshot upload --lang java --bucket runner-codes
4. Test Execution
sudo infra.operator host --lang java --code "public class Main { public static void main(String[] args) { System.out.println(\"Hello from Java\"); } }" --mem 512 --vcpus 1 --snapshot
Execution Flow
Examples
Hello World
Request
{
"trace_id": "java-hello-001",
"lang": "java",
"code": "public class Main {\n public static void main(String[] args) {\n System.out.println(\"Hello from Java!\");\n }\n}",
"timeout": 30
}
Response
{
"trace_id": "java-hello-001",
"stdout": "Hello from Java!\n",
"stderr": "",
"exit_code": 0
}
Variables and Calculations
Request
{
"trace_id": "java-calc-001",
"lang": "java",
"code": "public class Main {\n public static void main(String[] args) {\n int x = 10;\n int y = 20;\n System.out.println(\"Sum: \" + (x + y));\n System.out.println(\"Product: \" + (x * y));\n }\n}",
"timeout": 30
}
Response
{
"trace_id": "java-calc-001",
"stdout": "Sum: 30\nProduct: 200\n",
"stderr": "",
"exit_code": 0
}
Classes and Objects
Request
{
"trace_id": "java-class-001",
"lang": "java",
"code": "class Calculator {\n private int result = 0;\n \n Calculator add(int x) { result += x; return this; }\n Calculator multiply(int x) { result *= x; return this; }\n int getResult() { return result; }\n}\n\npublic class Main {\n public static void main(String[] args) {\n Calculator calc = new Calculator();\n int result = calc.add(5).multiply(3).add(10).getResult();\n System.out.println(\"Result: \" + result);\n }\n}",
"timeout": 30
}
Response
{
"trace_id": "java-class-001",
"stdout": "Result: 25\n",
"stderr": "",
"exit_code": 0
}
Collections
Request
{
"trace_id": "java-list-001",
"lang": "java",
"code": "import java.util.*;\n\npublic class Main {\n public static void main(String[] args) {\n List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);\n int sum = numbers.stream().mapToInt(Integer::intValue).sum();\n System.out.println(\"Numbers: \" + numbers);\n System.out.println(\"Sum: \" + sum);\n }\n}",
"timeout": 30
}
Response
{
"trace_id": "java-list-001",
"stdout": "Numbers: [1, 2, 3, 4, 5]\nSum: 15\n",
"stderr": "",
"exit_code": 0
}
Exception Handling
Request
{
"trace_id": "java-exception-001",
"lang": "java",
"code": "public class Main {\n public static void main(String[] args) {\n try {\n int result = 10 / 0;\n } catch (ArithmeticException e) {\n System.out.println(\"Caught: \" + e.getMessage());\n } finally {\n System.out.println(\"Cleanup complete\");\n }\n }\n}",
"timeout": 30
}
Response
{
"trace_id": "java-exception-001",
"stdout": "Caught: / by zero\nCleanup complete\n",
"stderr": "",
"exit_code": 0
}
Complex Test: Comprehensive Java
Request
{
"trace_id": "java-complex-001",
"lang": "java",
"code": "import java.util.*;\nimport java.util.stream.*;\n\npublic class Main {\n static Map<Integer, Long> memo = new HashMap<>();\n \n public static void main(String[] args) {\n System.out.println(\"=== Java Complex Test ===\");\n System.out.println();\n \n // Test 1: Fibonacci with memoization\n System.out.println(\"1. Fibonacci with memoization:\");\n List<Long> fibs = IntStream.range(0, 15)\n .mapToObj(Main::fib)\n .collect(Collectors.toList());\n System.out.println(\" First 15: \" + fibs);\n System.out.println(\" Fib(50) = \" + fib(50));\n \n // Test 2: QuickSort\n System.out.println();\n System.out.println(\"2. QuickSort:\");\n int[] arr = {64, 34, 25, 12, 22, 11, 90};\n System.out.println(\" Input: \" + Arrays.toString(arr));\n quickSort(arr, 0, arr.length - 1);\n System.out.println(\" Output: \" + Arrays.toString(arr));\n \n // Test 3: Collections and Streams\n System.out.println();\n System.out.println(\"3. Streams and Collections:\");\n List<Integer> numbers = IntStream.rangeClosed(1, 10).boxed().collect(Collectors.toList());\n List<Integer> squares = numbers.stream().map(x -> x * x).collect(Collectors.toList());\n int sum = squares.stream().mapToInt(Integer::intValue).sum();\n System.out.println(\" Numbers: \" + numbers);\n System.out.println(\" Squares: \" + squares);\n System.out.println(\" Sum: \" + sum);\n \n // Test 4: Map operations\n System.out.println();\n System.out.println(\"4. Map operations:\");\n Map<String, Integer> ages = new LinkedHashMap<>();\n ages.put(\"Alice\", 30);\n ages.put(\"Bob\", 25);\n ages.put(\"Charlie\", 35);\n ages.forEach((k, v) -> System.out.println(\" \" + k + \": \" + v));\n double avg = ages.values().stream().mapToInt(Integer::intValue).average().orElse(0);\n System.out.println(\" Average age: \" + avg);\n \n // Test 5: Classes and inheritance\n System.out.println();\n System.out.println(\"5. Polymorphism:\");\n Animal[] animals = {new Dog(\"Rex\"), new Cat(\"Whiskers\"), new Dog(\"Buddy\")};\n for (Animal a : animals) {\n System.out.println(\" \" + a.speak());\n }\n \n // Test 6: Optional and functional\n System.out.println();\n System.out.println(\"6. Optional handling:\");\n Optional<String> opt1 = Optional.of(\"Hello\");\n Optional<String> opt2 = Optional.empty();\n System.out.println(\" Present: \" + opt1.orElse(\"default\"));\n System.out.println(\" Empty: \" + opt2.orElse(\"default\"));\n \n // Test 7: String operations\n System.out.println();\n System.out.println(\"7. String operations:\");\n String text = \"Hello, World! Welcome to Java.\";\n System.out.println(\" Original: \" + text);\n System.out.println(\" Upper: \" + text.toUpperCase());\n System.out.println(\" Words: \" + text.split(\" \").length);\n System.out.println(\" Reversed: \" + new StringBuilder(text).reverse());\n \n // Test 8: Exception handling\n System.out.println();\n System.out.println(\"8. Exception handling:\");\n try {\n int result = divide(10, 0);\n } catch (ArithmeticException e) {\n System.out.println(\" Caught: \" + e.getMessage());\n }\n System.out.println(\" Safe divide: \" + divide(10, 2));\n \n System.out.println();\n System.out.println(\"=== All tests passed ===\");\n }\n \n static long fib(int n) {\n if (memo.containsKey(n)) return memo.get(n);\n long result = (n <= 1) ? n : fib(n-1) + fib(n-2);\n memo.put(n, result);\n return result;\n }\n \n static void quickSort(int[] arr, int low, int high) {\n if (low < high) {\n int pi = partition(arr, low, high);\n quickSort(arr, low, pi - 1);\n quickSort(arr, pi + 1, high);\n }\n }\n \n static int partition(int[] arr, int low, int high) {\n int pivot = arr[high];\n int i = low - 1;\n for (int j = low; j < high; j++) {\n if (arr[j] < pivot) {\n i++;\n int temp = arr[i]; arr[i] = arr[j]; arr[j] = temp;\n }\n }\n int temp = arr[i+1]; arr[i+1] = arr[high]; arr[high] = temp;\n return i + 1;\n }\n \n static int divide(int a, int b) {\n return a / b;\n }\n}\n\nabstract class Animal {\n String name;\n Animal(String name) { this.name = name; }\n abstract String speak();\n}\n\nclass Dog extends Animal {\n Dog(String name) { super(name); }\n String speak() { return name + \" says Woof!\"; }\n}\n\nclass Cat extends Animal {\n Cat(String name) { super(name); }\n String speak() { return name + \" says Meow!\"; }\n}",
"timeout": 45
}
Response
{
"trace_id": "java-complex-001",
"stdout": "=== Java Complex Test ===\n\n1. Fibonacci with memoization:\n First 15: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377]\n Fib(50) = 12586269025\n\n2. QuickSort:\n Input: [64, 34, 25, 12, 22, 11, 90]\n Output: [11, 12, 22, 25, 34, 64, 90]\n\n3. Streams and Collections:\n Numbers: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]\n Squares: [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]\n Sum: 385\n\n4. Map operations:\n Alice: 30\n Bob: 25\n Charlie: 35\n Average age: 30.0\n\n5. Polymorphism:\n Rex says Woof!\n Whiskers says Meow!\n Buddy says Woof!\n\n6. Optional handling:\n Present: Hello\n Empty: default\n\n7. String operations:\n Original: Hello, World! Welcome to Java.\n Upper: HELLO, WORLD! WELCOME TO JAVA.\n Words: 5\n Reversed: .avaJ ot emocleW !dlroW ,olleH\n\n8. Exception handling:\n Caught: / by zero\n Safe divide: 5\n\n=== All tests passed ===\n",
"stderr": "",
"exit_code": 0
}
Performance
| Operation | Time |
|---|---|
| Compilation | ~2s |
| Hello World (total) | ~3s |
| Stream operations | ~100ms |
| JSON parsing | ~50ms |
Limitations
warning
The Java environment has the following limitations:
- Single file only: Must be self-contained in one Main.java
- No external JARs: Only standard library available
- Class name must be Main: The main class must be named Main
- No network: Network operations will fail
- Memory limit: 512 MiB default
Best Practices
Best Practices
- Name your class Main — Always name your main class
Mainfor proper execution. - Use full imports — Use full import statements for java.util, java.io, etc.
- Handle exceptions — Wrap risky operations in try-catch blocks for meaningful errors.
- Account for compilation — Set timeout to at least 60 seconds to account for JVM startup and compilation.