在java中查找Map时出现空点异常.

Question

这是代码:

import java.security.InvalidParameterException;
import java.util.HashMap;
import java.util.Map;

/**
 * Created by IDEA on 13/06/15.
 */
public class ShiftCodes {
    private final Map<byte[], Byte> shiftMap;

    public ShiftCodes(int[][] collapseMatrix) {
        shiftMap = new HashMap<byte[], Byte>();
        for (int i = -128; i < 128; i++) {
            for (int j = -128; i < 128; i++) {
                byte b1 = (byte) i;
                byte b2 = (byte) j;
                byte[] k = new byte[] {b1, b2};
                Byte v = new Byte(GenoBytes.genoByte(GenoBytes.collapse(
                        b1, b2, collapseMatrix)));
                shiftMap.put(k, v);
            }
        }
    }

    public ShiftCodes() {
        this(GenoBytes.defaultCollpaseMatrix);
    }

    public byte lookup(byte b1, byte b2) {
        return shiftMap.get(new byte[] {b1, b2}).byteValue();
    }

    public byte[] lookup(byte[] bs1, byte[] bs2) {
        if(bs1.length != bs2.length) {
            throw new InvalidParameterException("bs1 and bs2 must be of the same length");
        }
        byte[] res = new byte[bs1.length];
        for(int i = 0; i < bs1.length; i++) {
            res[i] = lookup(bs1[i], bs2[i]);
        }
        return res;
    }

    public static void main(String[] args) {
        ShiftCodes shiftCodes1 = new ShiftCodes();
        ShiftCodes shiftCodes2 = new ShiftCodes(GenoBytes.antidiangonal);
//        System.out.println(shiftCodes1.lookup((byte) 0b11, (byte) 0b01));
        System.out.println((int) shiftCodes1.shiftMap.get(new byte[] {(byte) 1, (byte) 0}));
    }
}

我正在做的只是在地图中查找某些内容,但是我收到了一个错误:

Exception in thread "main" java.lang.NullPointerException
    at vu.co.kaiyin.ShiftCodes.main(ShiftCodes.java:50)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)

Answer 1

数组只等于它们自己.这意味着将它们用作地图中的键将无法正常工作:

map.get(new byte[] {(byte) 1, (byte) 0})

将始终返回null.

您需要创建一个包含两个字节字段的类,equals()并hashCode()正确覆盖它,并将该类用作映射的键​​.