Conversion and Casting

Tracing technique for casting (primitive data types)
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byte ---> short ---> int ---> long ---> float ---> double
char ----> int ---> long ---> float ---> double

In the above chart, if you can trace path from one element to another element, then that cast is safe (or) implicit cast happens.
For ex: conversion of byte to float is fine as you can trace the path. Reverse (float to byte) is not safe as you cannot trace the path.

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Primitive Data Type - Conversion (Implicit Casting)
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For primitive data types, this happens in the following cases

1. Assignment operations
int i;
double d;
i=10;
d=i; // Implicit Casting happens here

2. Method call

int i=10;
foo(i); // Implicit Casting happens here

public void foo(long l) {
...
}

3. Arithment promotions
int i =10;
long l = 20;
long result = l/i; // Implicit Casting happens here as part of arithmetic promotions.

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Primitive Data Type - Explicit Casting
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int i;
long l;
l = (long) i; // Works - even though this is not necessary. Implicit cast happens if we don't specify it.
i = (int) l; // Explicit casting. Narrow down cast always needs Explicit casting. This compiles and works. But result could be unexpected as most significant bits will be lost.


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Object References - Conversion (Implicit Casting)
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TBD.

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Object References - Conversion (Explicit Casting)
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TBD.

Reference:
Java Certification Book.