实现Externalizable，这样可以最大限度地节省空间

Question

我有class元素，它有以下属性(参见class)。由于这两个整数值的范围非常小，所以我想把它们存储在一个短的地方。这对我不起作用。我想使用位移位。我在这里做错了什么？这是学校的作业，所以一定是短篇。

public class Element implements Externalizable {
    private static final long serialVersionUID = 6529685098267757690L;
    private boolean isMarked;
    private    boolean isValid;
   private boolean isDeleted;
    private int key; // VALUE AREA: 0-500
    private int value; // VALUE AREA: 1-10
    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        short val =0;
        if(this.isMarked) val|=1;
        val <<=1;
        if(this.isValid) val|=1;
        val <<=1;
        if(this.isDeleted) val|=1;
        val <<=4;
        val |=  this.value;
        val <<=9;
        val |= (short) this.key;
        out.writeShort(val);
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        short s = in.readShort();

        this.isMarked = s % 2==1;
        s >>= 1;
        this.isValid =s % 2==1;
        s >>>= 1;
        this.isDeleted = s % 2==1;
        s >>>= 4;
        this.value = s % 8;
        s >>>=9;
        this.value = s % 512;
    }

    @Override
    public String toString() {
        return "Element{" +
                "isMarked=" + isMarked +
                ", isValid=" + isValid +
                ", isDeleted=" + isDeleted +
                ", key=" + key +
                ", value=" + value +
                '}';
    }

    public Element(boolean isMarked, boolean isValid, boolean isDeleted, int key, int value) {
        this.isMarked = isMarked;
        this.isValid = isValid;
        this.isDeleted = isDeleted;
        this.key = key;
        this.value = value;
    }
    public Element(){}
}

Answer 1

以相反的顺序读取数据。使用二元and运算符而不是模运算符，因为short是有符号的。然后负数会导致您的评论中描述的问题。

将readExternal更改为：

@Override
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
    short s = in.readShort();

    this.key = s & 511; // masks the lower 9 bits
    s >>>= 9;
    this.value = s & 15; // masks the lower 4 bits
    s >>>= 4;
    this.isDeleted = (s & 1) == 1; 
    s >>>= 1;
    this.isValid = (s & 1) == 1;
    s >>>= 1;
    this.isMarked = (s & 1) == 1;
}