德.摩根De Morgan 和香农Shannon定理


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Java Base == & equals

  Tags:  Integer cache, == , equals This Blogger emphasizes that in actual development, developers should prioritize using .equals() to compare object values ​​rather than simply relying on == to compare references. Java's Integer cache mechanism provides memory optimization for Java programs with values ​​in the range of -128 to 127.However, values ​​outside this range will result in the creation of new objects, resulting in unexpected results in == comparisons.       public static void main(String[] args) {         Integer a = 228;         Integer b = 228;         System.out.println(a == b); // false         Integer x = 1;         Integer y = 1;         System.out.println(x == y); // true         Integer c = 228;         Integer d = 228;         System.out.println(System.identityHash...
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Double.NaN Float.NaN

Double.NaN  Float.NaN double i = 0.0/0.0; double i = Double.NaN; equals http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html public boolean equals( Object  obj) Compares this object against the specified object. The result is true if and only if the argument is not null and is a Double object that represents a double that has the same value as the double represented by this object. For this purpose, two double values are considered to be the same if and only if the method doubleToLongBits(double) returns the identical long value when applied to each. Note that in most cases, for two instances of class Double , d1 and d2 , the value of d1.equals(d2) is true if and only if d1.doubleValue() == d2.doubleValue() also has the value true . However, there are two exceptions: If d1 and d2 both represent Double.NaN , then the equals method returns true , even though Double.NaN==Double.NaN has the value ...
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