牛客網(wǎng)：為什么不能將實數(shù)作為 HashMap 的 key？

import?java.util.HashMap;import java.util.Map;//class?Point?{//????int?x;//????int?y;//????Point(int?a,?int?b)?{?x?=?a;?y?=?b;?}//}
public?class?Solution?{????public?int?maxPoints(Point[]?points)?{????????if?(points.length?<=?2)?{????????????return?points.length;????????}????????int?max?=?2;????????for?(int?i?=?0;?i?1;?i++)?{????????????Map?map?=?new?HashMap<>(16);????????????//?記錄垂直點數(shù);?當前和Points[i]在一條線上的最大點數(shù);?和Points[i]垂直的點數(shù)????????????int?ver?=?0,?cur,?dup?=?0;????????????for?(int?j?=?i?+?1;?j?????????????????if?(points[j].x?==?points[i].x)?{????????????????????if?(points[j].y?!=?points[i].y)?{????????????????????????ver++;????????????????????}?else?{????????????????????????dup++;????????????????????}????????????????}?else?{????????????????????float?d?=?(float)((points[j].y?-?points[i].y)?/?(double)?(points[j].x?-?points[i].x));????????????????????map.put(d,?map.get(d)?==?null???1?:?map.get(d)?+?1);????????????????}????????????}????????????cur?=?ver;????????????for?(int?v?:?map.values())?{????????????????cur?=?Math.max(v,?cur);????????????}????????????max?=?Math.max(max,?cur?+?dup?+?1);????????}????????return?max;????}}

public?static?void?main(String[]?args)?{????int[][]?vals?=?{{2,3},{3,3},{-5,3}};????Point[]?points?=?new?Point[3];????for?(int?i=0;?i????????points[i]?=?new?Point(vals[i][0],?vals[i][1]);????}????Solution?solution?=?new?Solution();????System.out.println(solution.maxPoints(points));}

System.out.println(0.0 == -0.0);

map.put(d, map.get(d) == null ? 1 : map.get(d) + 1);

public?V?get(Object?key)?{????Node?e;????return?(e?=?getNode(hash(key),?key))?==?null???null?:?e.value;}

static?final?int?hash(Object?key)?{????int?h;????return?(key?==?null)???0?:?(h?=?key.hashCode())?^?(h?>>>?16);}

public native int hashCode();

public?static?void?main(String[]?args)?{????????System.out.println(0.0?==?-0.0);????????System.out.println(new?Float(0.0).hashCode()?==?????????????new?Float(-0.0).hashCode());    }

System.out.println(new?Float(0.0).equals(0.0f));System.out.println(new Float(0.0).equals((float) -0.0));

public?boolean?equals(Object?obj)?{????return?(obj?instanceof?Float)???????????&&?(floatToIntBits(((Float)obj).value)?==????????????????????floatToIntBits(value));}

/*** Returns a representation of the specified floating-point value* according to the IEEE 754 floating-point "single format" bit* layout.** 
Bit 31 (the bit that is selected by the mask* {@code 0x80000000}) represents the sign of the floating-point* number.* Bits 30-23 (the bits that are selected by the mask* {@code 0x7f800000}) represent the exponent.* Bits 22-0 (the bits that are selected by the mask* {@code 0x007fffff}) represent the significand (sometimes called* the mantissa) of the floating-point number.** 
If the argument is positive infinity, the result is* {@code 0x7f800000}.** 
If the argument is negative infinity, the result is* {@code 0xff800000}.** 
If the argument is NaN, the result is {@code 0x7fc00000}.** 
In all cases, the result is an integer that, when given to the* {@link #intBitsToFloat(int)} method, will produce a floating-point* value the same as the argument to {@code floatToIntBits}* (except all NaN values are collapsed to a single* "canonical" NaN value).** @param   value   a floating-point number.* @return the bits that represent the floating-point number.*/public static int floatToIntBits(float value) {    int result = floatToRawIntBits(value);    // Check for NaN based on values of bit fields, maximum    // exponent and nonzero significand.    if (((result & FloatConsts.EXP_BIT_MASK) ==          FloatConsts.EXP_BIT_MASK) &&         (result & FloatConsts.SIGNIF_BIT_MASK) != 0)        result = 0x7fc00000;    return result;}

System.out.println(Float.floatToIntBits((float)?0.0));System.out.println(Float.floatToIntBits((float)?-0.0));System.out.println(Float.floatToRawIntBits(0.0f));System.out.println(Float.floatToRawIntBits((float)-0.0));

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