Boolean为final修饰，不能被继承，实现了java.io.Serializable接口和Comparable<Boolean>接口，可以序列化和进行比较，Boolean没有无参构造器

源码

public final class Boolean implements java.io.Serializable,
                                      Comparable<Boolean>
{
    // //因为Boolean就只有两个值，故直接在jvm启动时便生成这两个值并建立引用
    public static final Boolean TRUE = new Boolean(true);

    public static final Boolean FALSE = new Boolean(false);

    public static final Class<Boolean> TYPE = (Class<Boolean>) Class.getPrimitiveClass("boolean");

    public Boolean(boolean value) {
        this.value = value;
    }

    // Boolean有一个可以传入字符串的构造器，只当字符串为“true”时，value为true，其余都为false
    public Boolean(String s) {
        this(parseBoolean(s));
    }

    public static boolean parseBoolean(String s) {
        // 只要name不为true，统一返回false
        return ((s != null) && s.equalsIgnoreCase("true"));
    }

    public boolean booleanValue() {
        return value;
    }

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

    public static Boolean valueOf(String s) {
        return parseBoolean(s) ? TRUE : FALSE;
    }

    public static String toString(boolean b) {
        return b ? "true" : "false";
    }

    public String toString() {
        return value ? "true" : "false";
    }

    @Override
    public int hashCode() {
        // Boolean的哈希值只有固定的两个值，true为1231，false为1237
        return Boolean.hashCode(value);
    }

    public static int hashCode(boolean value) {
        return value ? 1231 : 1237;
    }

    public boolean equals(Object obj) {
        if (obj instanceof Boolean) {
            return value == ((Boolean)obj).booleanValue();
        }
        return false;
    }

    public static boolean getBoolean(String name) {
        boolean result = false;
        try {
            result = parseBoolean(System.getProperty(name));
        } catch (IllegalArgumentException | NullPointerException e) {
        }
        return result;
    }

    public int compareTo(Boolean b) {
        return compare(this.value, b.value);
    }

    public static int compare(boolean x, boolean y) {
        return (x == y) ? 0 : (x ? 1 : -1);
    }

    public static boolean logicalAnd(boolean a, boolean b) {
        return a && b;
    }

    public static boolean logicalOr(boolean a, boolean b) {
        return a || b;
    }

    public static boolean logicalXor(boolean a, boolean b) {
        return a ^ b;
    }
}

总结

• 如果一个类只有有限的几种状态，考虑用几个final的静态变量来表示不同状态的实例。例如编写一个Weekday类，状态只有7个，就不要让用户写new Weekday(1)，直接提供Weekday.MONDAY即可
• 推荐的形式是Boolean.TRUE或Boolean.valueOf(true)或Boolean.valueOf("true")，避免生成不必要的对象

实验室

Boolean boo = new Boolean(true);
System.err.println(boo == Boolean.TRUE); // false