ByteCodeIterator.java

package main.coding_170416.jvm.loader;

import main.coding_170416.jvm.util.Util;

import java.util.Arrays;

/**
 * Created by peter on 2017/4/21.
 */
public class ByteCodeIterator {
    byte[] codes;
    int pos = 0;

    ByteCodeIterator(byte[] codes){
        this.codes = codes;
    }
    public byte[] getBytes(int len){
        if(pos+len>=codes.length){
            throw new ArrayIndexOutOfBoundsException();
        }
        byte[] data = Arrays.copyOfRange(codes,pos,pos+len);
        pos+=len;
        return data;
    }

    public int nextU1ToInt(){
        return Util.byteToInt(new byte[]{codes[pos++]});
    }

    public int nextU2ToInt(){
        return Util.byteToInt(new byte[]{codes[pos++],codes[pos++]});
    }

    public int nextU4ToInt(){
        return Util.byteToInt(new byte[]{codes[pos++],codes[pos++],codes[pos++],codes[pos++]});
    }

    public String nextU4ToHexString(){
        return Util.byteToHexString(new byte[]{codes[pos++],codes[pos++],codes[pos]++,codes[pos++]});
    }

    public String nextUxToHexString(int len){
        byte[] temp = new byte[len];

        for(int i=0;i<len;i++){
            temp[i] = codes[pos++];
        }
        return Util.byteToHexString(temp).toLowerCase();
    }

    public void back(int n){
        this.pos-=n;
    }
}