java基础类库学习（一.5）BigDecimal类

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Bigdecimal解决double/float的精度丢失，使用Bigdecimal类创建BigDecimal实例时，一定用字符串作为构造器的参数，才不会发生精度损失，若使用duoble则依旧会存在精度损失

BigDecimal类源码？

public class BigDecimal extends Number implements Comparable<BigDecimal> {

private final BigInteger intVal;

private final int scale; 

private transient int precision;

private transient String stringCache;

static final long INFLATED = Long.MIN_VALUE;

private static final BigInteger INFLATED_BIGINT = BigInteger.valueOf(INFLATED);

private static final long serialVersionUID = 6108874887143696463L;

BigDecimal(BigInteger intVal, long val, int scale, int prec) {
    this.scale = scale;
    this.precision = prec;
    this.intCompact = val;
    this.intVal = intVal;
}

public BigDecimal(char[] in, int offset, int len) {
    this(in,offset,len,MathContext.UNLIMITED);
}

public BigDecimal(char[] in) {
    this(in, 0, in.length);
}

public BigDecimal(String val) {//该构造器推荐使用
    this(val.toCharArray(), 0, val.length());
}

public BigDecimal(double val) {//不推荐使用该构造器，因为存在一定的不可预知性
    this(val,MathContext.UNLIMITED);
}

public BigDecimal(BigInteger val) {
    scale = 0;
    intVal = val;
    intCompact = compactValFor(val);
}

public BigDecimal add(BigDecimal augend) {//提供的加法运算
    if (this.intCompact != INFLATED) {
        if ((augend.intCompact != INFLATED)) {
            return add(this.intCompact, this.scale, augend.intCompact, augend.scale);
        } else {
            return add(this.intCompact, this.scale, augend.intVal, augend.scale);
        }
    } else {
        if ((augend.intCompact != INFLATED)) {
            return add(augend.intCompact, augend.scale, this.intVal, this.scale);
        } else {
            return add(this.intVal, this.scale, augend.intVal, augend.scale);
        }
    }
}

public BigDecimal subtract(BigDecimal subtrahend) {//提供的减法运算
    if (this.intCompact != INFLATED) {
        if ((subtrahend.intCompact != INFLATED)) {
            return add(this.intCompact, this.scale, -subtrahend.intCompact, subtrahend.scale);
        } else {
            return add(this.intCompact, this.scale, subtrahend.intVal.negate(), subtrahend.scale);
        }
    } else {
        if ((subtrahend.intCompact != INFLATED)) {
            // Pair of subtrahend values given before pair of
            // values from this BigDecimal to avoid need for
            // method overloading on the specialized add method
            return add(-subtrahend.intCompact, subtrahend.scale, this.intVal, this.scale);
        } else {
            return add(this.intVal, this.scale, subtrahend.intVal.negate(), subtrahend.scale);
        }
    }
}

public BigDecimal multiply(BigDecimal multiplicand) {//提供的乘法运算
    int productScale = checkScale((long) scale + multiplicand.scale);
    if (this.intCompact != INFLATED) {
        if ((multiplicand.intCompact != INFLATED)) {
            return multiply(this.intCompact, multiplicand.intCompact, productScale);
        } else {
            return multiply(this.intCompact, multiplicand.intVal, productScale);
        }
    } else {
        if ((multiplicand.intCompact != INFLATED)) {
            return multiply(multiplicand.intCompact, this.intVal, productScale);
        } else {
            return multiply(this.intVal, multiplicand.intVal, productScale);
        }
    }
}

public BigDecimal divide(BigDecimal divisor, RoundingMode roundingMode) {//提供的除法运算
    return this.divide(divisor, scale, roundingMode.oldMode);
}