ByteArrayOutputStream 里的问题

Question

private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;//为什么-8？Integer的MAX_VALUE在32位系统中位2^15-1,在64位系统中位2^31-1

 package ByteArrayOutputStream;

import java.io.IOException;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.util.Arrays;

/**
 * 字符缓冲流
 * @author Administrator
 *
 */
public class MyByteArrayOutputStream  extends OutputStream{
    public byte buf[];//字节缓冲区
    public int count;//写入的字节数
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;//为什么-8？Integer的MAX_VALUE在32位系统中位2^15-1,在64位系统中位2^31-1
    public MyByteArrayOutputStream() {
        this(32);//初始值为啥是32
    }
    public MyByteArrayOutputStream(int size){
        if(size < 0){
            throw new IllegalArgumentException("错误的初始化大小" + size);
        }
        buf = new byte[size];
    }
    private void ensureCapacity(int minCapacity){
        if(minCapacity - buf.length > 0){//r如果将要添加的值超过了byte的数组的长度将原数组增长
            grow(minCapacity);
        }
    }
    private void grow(int minCapacity){//2^30+1  2^31
        int oldCapacity = buf.length;//2^30 2^31-1
        int newCapacity = oldCapacity << 1;//容量增长为原来的两倍2^31
        if(newCapacity - minCapacity < 0){
            newCapacity = minCapacity;//新增长的容量小于添加后的实际容量，将容量增长为实际容量
        }
        if(newCapacity - MAX_ARRAY_SIZE > 0){//新增长的容量大于最大容量
            newCapacity = hugeCapacity(minCapacity);
        }
        System.out.println(newCapacity);
        buf = Arrays.copyOf(buf,newCapacity);//将数组的内容考到新的数组中
    }
    private static int hugeCapacity(int minCapacity){
        if(minCapacity < 0){
            throw new OutOfMemoryError();//内存溢出,为什么要抛出内存溢出
        }
        return (minCapacity > MAX_ARRAY_SIZE) ? Integer.MAX_VALUE : MAX_ARRAY_SIZE;//设置数组的最大容量为Integer.MAX_VAL
    }

    public synchronized void write(int b){
        ensureCapacity(count + 1);
        buf[count] = (byte)b;
        count +=1;
    }
    public synchronized void write(byte b [],int off,int len){
        if((off < 0) || (off > b.length) || (len < 0) || ((off + len ) - b.length > 0)){
            throw new IndexOutOfBoundsException();
        }
        ensureCapacity(count + len);
        System.arraycopy(b, off, buf, count, len);
        count +=len;
    }
    public synchronized void  writeTo(OutputStream out)throws IOException{
        out.write(buf, 0, count);
    }
    public synchronized void reset(){
        count  = 0;
    }
    public synchronized byte toByteArray()[]{
        return Arrays.copyOf(buf, count);
    }
    public synchronized int size(){
        return count;
    }
    public synchronized String toString(){
        return new String(buf,0,count);
    }
    public synchronized String toString(String charsetName) throws UnsupportedEncodingException{
        return new String(buf,0,count,charsetName);
    }
    @Deprecated
    public synchronized String toString(int hibyte){
        return new String(buf,hibyte,0,count);
    }
    public void close() throws IOException{}
}

Answer 1

http://blog.csdn.net/elsa_rong/article/details/49644245