JAVATM- The Beginnings
Java is a strongly typed language, which means all variables are given types, and that the type of each variable cannot be changed.
For compatible primitive data types, Java will implicitly convert a literal, variable, expression, or method return from the smaller type to the larger type. This is called a widening conversion, because the new data type is wider than the original type, so no information is lost.
In the example below, the variable b is of primitive type byte which occupies one byte of memory. It contains the decimal value 20, which is the value 14 in hexadecimal. When the byte variable b is assigned to int variable i, Java implicitly performs a widening conversion and copies the value of the byte into the lowest byte of the memory occupied by int variable i. The upper three bytes of i contain zero. When printed, both variables display the value 20.
All integer and floating point primitive types are compatible. An integer type will be implicitly converted to a floating point type. When this occurs, the fractional component of the floating point number is zero.
int i = 20;
float f = i; // Implicitly performs widening conversion
System.out.println(i); // Prints 20
System.out.println(f); // Prints 20.0
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