package java.lang;
import java.util.*;
/**
This interface imposes a total ordering on the objects of each class that implements it.
#對所有實現Comparable接口的每一個類的全部對象進行強排序.
This ordering is referred to as the class's <i>natural ordering</i>,
#這種排序被稱爲類的自然排序,
and the class's {@code compareTo} method is referred to as its <i>natural comparison method</i>.<p>
#類的方法compareTo()被稱爲它的自然比較方法.
Lists (and arrays) of objects that implement this interface can be sorted automatically by {@link Collections#sort(List) Collections.sort} (and{@link Arrays#sort(Object[]) Arrays.sort}).
#實現了Comparable接口的集合(數組)可通過Collections.sort(Arrays.sort)自動排序.
Objects that implement this interface can be used as keys in a {@linkplain SortedMap sorted map} or as elements in a {@linkplain SortedSet sorted set}, without the need to specify a {@linkplain Comparator comparator}.<p>
The natural ordering for a class {@code C} is said to be <i>consistent
with equals</i> if and only if {@code e1.compareTo(e2) == 0} has
the same boolean value as {@code e1.equals(e2)} for every
{@code e1} and {@code e2} of class {@code C}. Note that {@code null}
is not an instance of any class, and {@code e.compareTo(null)} should
throw a {@code NullPointerException} even though {@code e.equals(null)}
returns {@code false}.<p>
It is strongly recommended (though not required) that natural orderings be
consistent with equals. This is so because sorted sets (and sorted maps)
without explicit comparators behave "strangely" when they are used with
elements (or keys) whose natural ordering is inconsistent with equals. In
particular, such a sorted set (or sorted map) violates the general contract
for set (or map), which is defined in terms of the {@code equals}
method.<p>
For example, if one adds two keys {@code a} and {@code b} such that
{@code (!a.equals(b) && a.compareTo(b) == 0)} to a sorted
set that does not use an explicit comparator, the second {@code add}
operation returns false (and the size of the sorted set does not increase)
because {@code a} and {@code b} are equivalent from the sorted set's
perspective.<p>
Virtually all Java core classes that implement {@code Comparable} have natural
orderings that are consistent with equals. One exception is
{@code java.math.BigDecimal}, whose natural ordering equates
{@code BigDecimal} objects with equal values and different precisions
(such as 4.0 and 4.00).<p>
For the mathematically inclined, the <i>relation</i> that defines
the natural ordering on a given class C is:<pre>{@code
{(x, y) such that x.compareTo(y) <= 0}.
}</pre> The <i>quotient</i> for this total order is: <pre>{@code
{(x, y) such that x.compareTo(y) == 0}.
}</pre>
It follows immediately from the contract for {@code compareTo} that the
quotient is an <i>equivalence relation</i> on {@code C}, and that the
natural ordering is a <i>total order</i> on {@code C}. When we say that a
class's natural ordering is <i>consistent with equals</i>, we mean that the
quotient for the natural ordering is the equivalence relation defined by
the class's {@link Object#equals(Object) equals(Object)} method:<pre>
{(x, y) such that x.equals(y)}. </pre><p>
This interface is a member of the
<a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
Java Collections Framework</a>.
@param <T> the type of objects that this object may be compared to
@author Josh Bloch
@see java.util.Comparator
@since 1.2
*/
public interface Comparable<T> {
/**
#爲了排序 對象和指定的對象比較 .
Compares this object with the specified object for order.
#返回一個負數, 零, 或一個正數 對應的是這個對象小於, 等於, 或大於指定的對象.
Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.
#實現者還必須確保:
#對於所有的x,y : sgn(x.compareTo(y)) == -sgn(y.compareTo(x)).
#(這意味着: 當且僅當y.compareTo(x) 拋異常時, x.compareTo(y) 必然拋異常.)
<p>The implementor must ensure :
{@code sgn(x.compareTo(y)) == -sgn(y.compareTo(x))} for all {@code x} and {@code y}.
(This implies that {@code x.compareTo(y)} must throw an exception iff {@code y.compareTo(x)} throws an exception.)
#實現者還必須確保該關係是可傳遞的: x>y && y>z 必然 x>z
<p>The implementor must also ensure that the relation is transitive:
{@code (x.compareTo(y) > 0 && y.compareTo(z) > 0)} implies {@code x.compareTo(z) > 0}.
#最後,實現者還必須確保: x.compareTo(y)==0 表示 sgn(x.compareTo(z)) == sgn(y.compareTo(z))
<p>Finally, the implementor must ensure that {@code x.compareTo(y)==0}
implies that {@code sgn(x.compareTo(z)) == sgn(y.compareTo(z))}, for all {@code z}.
#強烈建議, 但不嚴格要求, (x.compareTo(y)==0) == (x.equals(y))
# 一般來說，任何實現Comparable接口並違反此條件的類應明確指出這一事實。
#推薦的語言是“注意：此類的自然排序與等式不一致”。
<p>It is strongly recommended, but not strictly required that {@code (x.compareTo(y)==0) == (x.equals(y))}.
Generally speaking, any class that implements the {@code Comparable} interface and violates this condition should clearly indicate this fact.
The recommended language is "Note: this class has a natural ordering that is inconsistent with equals."
#在前面的描述中，符號sgn()表達式指定數學signum函數，該函數定義爲返回{@code -1}之一，{@code 0}還是{@code 1}，具體取決於表達式的值分別爲負，零或正。
<p>In the foregoing description, the notation {@code sgn(}<i>expression</i>{@code )} designates the mathematical <i>signum</i> function,
which is defined to return one of {@code -1}, {@code 0}, or {@code 1} according to whether the value of <i>expression</i> is negative, zero, or positive, respectively.
@param o the object to be compared.
@return a negative integer, zero, or a positive integer as this object
is less than, equal to, or greater than the specified object.
@throws NullPointerException if the specified object is null
@throws ClassCastException if the specified object's type prevents it
from being compared to this object.
*/
public int compareTo(T o);
}
數學: 符號函數
x>0, sgnx= 1
x=0, sgnx= 0
x<0, sgnx=-1