java – 盒装布尔值的等价

发布时间：2020-12-15 04:45:17 所属栏目：Java 来源：网络整理

导读：快速提问：是否保证此代码始终显示为真？ Boolean b1 = true;Boolean b2 = true;System.out.println(b1 == b2); 拳击布尔似乎总是导致相同的布尔对象,但我找不到太多关于JLS中的盒装布尔相等的信息.相反,它甚至似乎暗示拳击应该创建新对象,甚至可能导致OOM异

快速提问：是否保证此代码始终显示为真？

Boolean b1 = true;
Boolean b2 = true;
System.out.println(b1 == b2);

拳击布尔似乎总是导致相同的布尔对象,但我找不到太多关于JLS中的盒装布尔相等的信息.相反,它甚至似乎暗示拳击应该创建新对象,甚至可能导致OOM异常.

你的想法是什么？

解决方法

从 Java Language Specification on Boxing Conversion

Boxing conversion converts expressions of primitive type to
corresponding expressions of reference type. Specifically,the
following nine conversions are called the boxing conversions:

From type boolean to type Boolean

[…]

If the value p being boxed is an integer literal of type int between
-128 and 127 inclusive (§3.10.1),or the boolean literal true or false (§3.10.3),or a character literal between 'u0000' and 'u007f'
inclusive (§3.10.4),then let a and b be the results of any two boxing
conversions of p. It is always the case that a == b.

这相对简单就像implemented那样

/**
 * The {@code Boolean} object corresponding to the primitive
 * value {@code true}.
 */
public static final Boolean TRUE = new Boolean(true);

/**
 * The {@code Boolean} object corresponding to the primitive
 * value {@code false}.
 */
public static final Boolean FALSE = new Boolean(false);

public static Boolean valueOf(boolean b) {
    return (b ? TRUE : FALSE);
}

（编辑：李大同）

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