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package io;
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import java.nio.ByteBuffer;
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public class MemoryDemo {
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    public static void main(String[] args) {
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        // on heap allocation
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        int[] heapArray = new int[1024]; // allocated on java heap
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        heapArray[0] = 42;
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        System.out.println("Heap Value: " + heapArray[0]);
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        // modern off heap allocation
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        ByteBuffer buffer = ByteBuffer.allocateDirect(4096);
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        buffer.putInt(0, 42);
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        int value = buffer.getInt(0);
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        System.out.println("Off Heap value: " + value);
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    }
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}

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package io;
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import java.nio.ByteBuffer;
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import java.nio.charset.StandardCharsets;
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import io.netty.buffer.ByteBuf;
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import io.netty.buffer.PooledByteBufAllocator;
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public class OffHeapAvoidFullGc {
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    public static void main(String[] args) {
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        int size = 50;
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        int totalBytes = size * 1024 * 1024 // mb
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        // 01. allocate off heap
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        ByteBuf buffer = PooledByteBufAllocator.DEFAULT.directBuffer(totalBytes);
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        // 02. 고정문자열로 데이터 채우기
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        try {
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            byte[] content = "BIG_DATA".getBytes(StandardCharsets.UTF_8);
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            for (i = 0; i < totalBytes/content.length; i++) {
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                buffer.writeBytes(content);
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            }
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        // 03. 읽기포인터 초기화, 일부 확인
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        buffer.setIndex(0, buffer.writerIndex())
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        byte[] preview = new byte[20];
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        buffer.readBytes(preview);
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        System.out.println("sample data :" + new String(preview));
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        } finally {
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            buffer.release();
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        }
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    }
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}