浮点数之间的等值判断，基本数据类型不能用==来比较，包装数据类型不能用equals来判断

float a =1.0f-0.9f;

float b =0.9f-0.8f;

if(a == b){

// 预期进入此代码快，执行其它业务逻辑

// 但事实上a==b的结果为false

}

Float x = Float.valueOf(a);

Float y = Float.valueOf(b);

if(x.equals(y)){

// 预期进入此代码快，执行其它业务逻辑

// 但事实上equals的结果为false

}

float a =1.0f-0.9f;

float b =0.9f-0.8f;

float diff =1e-6f;

if(Math.abs(a -b)<diff){

System.out.println("true");

}

BigDecimal a =new BigDecimal("1.0");

BigDecimal b =new BigDecimal("0.9");

BigDecimal c =new BigDecimal("0.8");

BigDecimal x = a.subtract(b);

BigDecimal y = b.subtract(c);

if(x.equals(y)){

System.out.println("true");

}