java Java中浮点“1”和浮点“1f”之间的区别是什么？
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What is the Difference between float "1" and float "1f" in Java?
提问by m4tx
Is there any difference - in Java - between defining float variables like, e.g., this: 1and this: 1f? Is the JVM doing any casts at run-time when I write 1, or something that could slow down my app?
在 Java 中，定义浮点变量（例如 this:1和 this: ）之间有什么区别1f吗？JVM 在运行时是否在执行任何强制转换1，或者可能会减慢我的应用程序的速度？
Regards
问候
回答by Jigar Joshi
1 is implicitly considered as intliteral where 1fis considered as floatliteral
1 被隐式视为int文字，其中1f被视为float文字
See
看
回答by vbezhenar
Java code
Java代码
float f1 = 1;
float f2 = 1f;
compiles to following bytecode:
编译为以下字节码：
0: fconst_1
1: fstore_1
2: fconst_1
3: fstore_2
As you can see, there's no difference at run-time.
如您所见，运行时没有区别。
回答by GuilhE
float a = 1;
float b = 1f;
It's the same, but if you do something like:
这是一样的，但如果你做这样的事情：
int a = 1f
Will throw "Type mismatch: cannot convert from float to int"
会抛出“类型不匹配：无法从浮点数转换为整数”
int b = 1d or 1.0
Will throw "Type mismatch: cannot convert from double to int"
会抛出“类型不匹配：无法从双精度转换为整数”
float c = 1d or 1.0
Will throw "Type mismatch: cannot convert from double to float"
Note that:
会抛出“Type mismatch: cannot convert from double to float”
注意：
double a = 2.0;
double b = 2d;
double c = 2.0f;
if (a == b) {
if (c == a) {
if (c == b) {
return 1;
}
}
}
Will return 1;
Regards.
将返回 1；
问候。
回答by Andreas Johansson
Basically 1will default to an int. If you write 1fit will be considered a float. If you write 1.0(no f) it will default to a double.
基本上1会默认为int. 如果你写1f它会被认为是一个float. 如果你写1.0(no f) 它将默认为double.
A floating-point literal is of type float if it is suffixed with an ASCII letter F or f; otherwise its type is double and it can optionally be suffixed with an ASCII letter D or d.
如果浮点字面量以 ASCII 字母 F 或 f 为后缀，则它属于 float 类型；否则它的类型是 double 并且可以选择以 ASCII 字母 D 或 d 为后缀。
回答by Crazenezz
If the case like this the JVM will pass it.
如果是这种情况，JVM 将通过它。
public class Test {
public static void main(String[] args) {
float f = 1;
System.out.println(f);
}
}
But it will occur exception if you do something like this:
但是如果你做这样的事情会发生异常：
public class Test {
public static void main(String[] args) {
float f = 1.5;
}
}
Exception:
例外：
Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - possible loss of precision
required: float
found: double
at package.Test.main(Test.java:17)
What we can analyze for this two example is, for the first example it automatically converted to float, but for the second example if you add some decimal point without the for Fsuffix than it will automatically converted to double.
对于这两个例子，我们可以分析的是，第一个例子它自动转换为float，但是对于第二个例子，如果你添加一些没有f或F后缀的小数点，它会自动转换为double。
回答by manurajhada
Yes, there is a big difference between 1and 1f. As you can't declare a variable without giving its type in java, Its clear 1is an intand 1fdenotes floatat compile time itself. This is nothing related to run time or slow down your app.
是的，1和之间有很大的区别1f。正如你不能没有在Java中给予其类型声明一个变量，它明确1是int和1f表示float在编译时间本身。这与运行时间或减慢应用程序无关。
