BigDecimal 类的 compareTo() 和 equals()方法

r囧r小猫 2023-09-30 15:43 34阅读 0赞

## BigDecimal 类的 compareTo() 和 equals()方法 ##

#### 1. compareTo()源码 ####

/**
        * Compares this BigDecimal with the specified BigDecimal. 
        * Two BigDecimal objects that are equal in value but have 
        * a different scale (like 2.0 and 2.00) are considered equal
        * by this method. This method is provided in preference to 
        * individual methods for each of the six boolean comparison 
        * operators（<,<=,==,>,>=,!=）. The suggested idiom for 
        * performing these comparisons is: x.compartTo(y) <op> 0, 
        * where <op> is one of the six comparison operators.
        * 
        * @param  val - BigDecimal to which this BigDecimal is to be 
        *         compared.
        * @return -1,0 or 1 as this BigDecimal is numerically less than,
        *         equal to, or greater than val.
        */
    public int compareTo(BigDecimal val) {
        
        // Quick path for equal scale and non-inflated case.
        if (scale == val.scale) {
        
            long xs = intCompact;
            long ys = val.intCompact;
            if (xs != INFLATED && ys != INFLATED)
                return xs != ys ? ((xs > ys) ? 1 : -1) : 0;
        }
        int xsign = this.signum();
        int ysign = val.signum();
        if (xsign != ysign)
            return (xsign > ysign) ? 1 : -1;
        if (xsign == 0)
            return 0;
        int cmp = compareMagnitude(val);
        return (xsign > 0) ? cmp : -cmp;
    }

##### 1.1 注释翻译 #####

将当前 BigDecimal 实例与给定 BigDecimal 实例进行比较。本方法认为，数值相同但精度不同（例如：2.0 和 2.00）的两个 BigDecimal 是相同的。

本方法的返回值总共有3种：

*  \-1 ：当前 BigDecimal 的数值小于给定的 BigDecimal。
 *  0 ：当前 BigDecimal 的数值等于给定的 BigDecimal。
 *  1 ：当前 BigDecimal 的数值大于给定的 BigDecimal。

##### 1.2 实现细节 #####

#### 2. equals()源码 ####

/**
     * Compares this BigDecimal with the specified Object for equality. 
     * Unlike compareTo, thi method considers two BigDecimal objects equal
     * only if they are equal in value and scale (thus 2.0 is not equal to 2.00
     * when compared by this method).
     * 
     * @param  x - Object to which this BigDecimal is to to compared.
     * @return   - true if and only if the specified Object is a BigDecimal whose 
     *             value and scale are equal to this BigDecimal`s.
     */
    @Override
    public boolean equals(Object x) {
        
        if (!(x instanceof BigDecimal))
            return false;
        BigDecimal xDec = (BigDecimal) x;
        if (x == this)
            return true;
        if (scale != xDec.scale)
            return false;
        long s = this.intCompact;
        long xs = xDec.intCompact;
        if (s != INFLATED) {
        
            if (xs == INFLATED)
                xs = compactValFor(xDec.intVal);
            return xs == s;
        } else if (xs != INFLATED)
            return xs == compactValFor(this.intVal);
    
        return this.inflated().equals(xDec.inflated());
    }

##### 2.1 注释翻译 #####

将当前 BigDecimal 实例与给定 BigDecimal 实例进行比较。本方法认为，只有数值和精度都相同的两个 BigDecimal 才是相同的（因此本方法认为2.0 和 2.00 是不同的）。

本方法的返回值总共有2种：

*  true ：当前 BigDecimal 的数值等于给定的 BigDecimal。
 *  false：当前 BigDecimal 的数值不等于给定的 BigDecimal。

##### 2.2 实现细节 #####

#### 3. 总结 ####

BigDecimal 类的 compartTo 方法和 equals 方法都能用于比较 BigDecimal 实例代表的数值的大小。但两个方法在判别两个数值是否相等的标准上存在一定的差异：compartTo 仅要求两个数的值（value）相等，equals 要求两个数的值和精度（scale）都要相等。

public static void main(String[] args) {
        
        BigDecimal b1 = new BigDecimal("2.0");
        BigDecimal b2 = new BigDecimal("2.00");
    
        System.out.println("b1.compareTo(b2):" + (b1.compareTo(b2) == 0));
        System.out.println("b1.equals(b2):" + b1.equals(b2));
    }
    b1.compareTo(b2):true
    b1.equals(b2):false
    
    Process finished with exit code 0