block.java

用JAVA实现的miniSQL

class Block {
    public String filename;   //文件名
    public long blockno;   //　文件块号
    public long head;  //　文件头大小
    public byte[] block;   //　块内容，一共4096个字节大小
    public int pos;
    public Block() {  
    	filename = null;
    	blockno = 0;
    	block = null;
    	head = 0;
    	pos = 0;
    }
    public Block(String fname, long bn, long hd, byte[] context) {
    	filename = fname;
    	blockno = bn;
    	head = hd;
        block = context;
        pos = 0;
    }
    public byte[] getByte()
    {
    	return block;
    }
    public int read(){
    	int a = block[pos];
    	pos++;
    	a=a&0x000000FF;
    	return a;
    }
    public void read(byte[] b){
    	for(int i=0 ;i<b.length; i++){
    		b[i]= block[pos];
    		pos++;
    	}
    }
    public void read(byte[] b,int len){
    	for(int i=0 ;i<b.length; i++){
    		b[i]= block[pos+i];
    	}
    	pos = pos+len;
    }
    public void readFully(byte[] b){
    	for(int i=0 ;i<b.length; i++){
    		b[i]= block[pos];
    		pos++;
    	}
    }
    public int readInt(){
    	int a = 0;
        for(int i = 0; i < 4; i ++) {
           int tmpVal = (block[pos+i] << (8 * (3-i)));
           switch (i) {
            case 0:
                tmpVal = tmpVal & 0xFF000000;
                break;
            case 1:
                tmpVal = tmpVal & 0x00FF0000;
                break;
            case 2:
                tmpVal = tmpVal & 0x0000FF00;
                break;
            case 3:
                tmpVal = tmpVal & 0x000000FF;
                break;
           }
           a = a | tmpVal;
        }
        pos = pos +4 ;
    	return a;
    }
    public float readFloat(){
    	int a = 0;
    	for(int i = 0; i < 4; i ++) {
           int tmpVal = (block[pos+i] << (8 * (3-i)));
           switch (i) {
            case 0:
                tmpVal = tmpVal & 0xFF000000;
                break;
            case 1:
                tmpVal = tmpVal & 0x00FF0000;
                break;
            case 2:
                tmpVal = tmpVal & 0x0000FF00;
                break;
            case 3:
                tmpVal = tmpVal & 0x000000FF;
                break;
           }
           a = a | tmpVal;
        }
        pos = pos +4 ;
    	return Float.intBitsToFloat(a);
    }
    public long readLong(){
    	long a = 0;
    	for(int i=0 ; i<8 ;i++,pos++){
    		a = a<<8;
    		a = a | (block[pos]&0xFF);
    	}
    	return a;
    }
    public boolean readBoolean(){
    	if(block[pos]==0){
    		pos++;
    		return false;
    	}
    	else{
    		pos++;
    		return true;
    	}
    }
    public void write(int a){
    	block[pos] = (byte)a;
    	pos++;
    }
    public void writeByte(byte a){
    	block[pos] = a;
    	pos++;
    }
    public void writeInt(int a){
    	block[pos]=(byte)((a&0xFF000000) >>> 24);
    	block[pos+1]=(byte)((a&0x00FF0000) >>> 16);
    	block[pos+2]=(byte)((a&0x0000FF00) >>> 8);
    	block[pos+3]=(byte)(a&0x000000FF);
    	pos = pos +4 ;
    }
    public void writeFloat(float a){
    	int temp = Float.floatToRawIntBits(a);
    	for(int i= 0; i<4;i++){
    		block[pos+3-i] = (byte)(temp&0xff);   
            temp = temp>>>8;   
    	}
    	pos = pos +4;
    }
    public void writeBoolean(boolean a){
    	if(a)
    		block[pos]=1;
    	else
    		block[pos]=0;
    	pos++;
    }
    public void writeLong(long a){
    	for(int i = 0; i< 8 ;i++){
    		block[pos+7-i]=(byte)(a&0xff);
    		a = a>>>8;
    	}
    	pos = pos + 8;
    }
    public void writeBytes(byte[] a){
    	for(int i = 0; i<a.length ; i++){
    		block[pos+i] = a[i];
    	}
    	pos = pos + a.length;
    }
    public void writeChars(String a){
    	byte[] b = a.getBytes();
    	for(int i = 0; i<b.length ; i++){
    		block[pos+2*i]=0;
    		block[pos+2*i+1]=b[i];
    	}
    	pos = pos + b.length*2;
    }
    public void writeChars(String a, int len){
    	byte[] b = a.getBytes();
    	for(int i = 0; i<b.length ; i++){
    		block[pos+2*i]=0;
    		block[pos+2*i+1]=b[i];
    	}
    	for(int i=b.length*2; i<len ; i++)
    		block[pos+i]=0;
    	pos = pos + len;
    }
    public void seek(int p){
    	pos = p;
    }
    public void writeZero(int len){
    	for(int i=0;i<len;i++)
    		block[pos++]=0;
    }
}