为什么 java 浮点文字不能提升为双倍，而我对包装器 class 做同样的事情？

Question

float num1 = 1.0;

This code does not compile because floating-point numbers are default double and it can not be assigned to smaller types unless explicitly casting.

Float num2 = new Float(2.0);

But this code is compiled perfectly even 2.0 is a double literal. Can anyone explain to me what is happening for the second sample?

Answer 1

If you look at the Class Float , you immediately get the answer:

public Float(double value) {
    this.value = (float)value;
}

btw you do need to do Float num2 = new Float(2.0); , Float num2 = 2.0f; is enough.