Java में Performance Optimization

public class Main {
	public static void main(String[] args) {
		// Run with: java -Xms256m -Xmx512m Main
		Runtime runtime = Runtime.getRuntime();
		System.out.println("Max heap: " + runtime.maxMemory() / (1024 * 1024) + "MB");
	}
}

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import java.util.*;
public class Main {
	public static void main(String[] args) {
		List<Integer> list = new ArrayList<>(); // fast sequential iteration/indexing
		Map<String, Integer> map = new HashMap<>(); // near O(1) lookup by key
		list.add(1);
		map.put("key", 1);
		System.out.println(list.get(0) + " " + map.get("key"));
	}
}

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public class Main {
	public static void main(String[] args) {
		StringBuilder sb = new StringBuilder(); // reuses one buffer instead of many temporary Strings
		for (int i = 0; i < 1000; i++) {
			sb.append(i);
		}
		System.out.println(sb.length());
	}
}

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import java.util.concurrent.*;
public class Main {
	public static void main(String[] args) {
		ExecutorService pool = Executors.newFixedThreadPool(4); // reused workers, not a new thread per task
		for (int i = 0; i < 8; i++) pool.submit(() -> {});
		pool.shutdown();
		System.out.println("8 tasks handled by 4 reused threads");
	}
}

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public class Main {
	static class ExpensiveResource {
		private static ExpensiveResource instance;
		static ExpensiveResource get() {
			if (instance == null) instance = new ExpensiveResource(); // deferred until first actually needed
			return instance;
		}
	}
	public static void main(String[] args) {
		System.out.println(ExpensiveResource.get() != null);
	}
}

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