From book OCA JAVA SE 7 Just as men and women are fundamentally different (according to John Gray, author of Men Are from Mars, Women Are from Venus), primitive variables and object reference variables differ from each other in multiple ways. The basic difference is that primitive variables store the actual values, whereas reference variables … Read more
In Joshua Bloch’s Effective Java, Item 5: “Avoid creating unnecessary objects”, he posts the following code example: public static void main(String[] args) { Long sum = 0L; // uses Long, not long for (long i = 0; i <= Integer.MAX_VALUE; i++) { sum += i; } System.out.println(sum); } and it takes 43 seconds to run. … Read more
The result of adding Java chars, shorts, or bytes is an int: Java Language Specification on Binary Numeric Promotion: If any of the operands is of a reference type, unboxing conversion (ยง5.1.8) is performed. Then: If either operand is of type double, the other is converted to double. Otherwise, if either operand is of type … Read more
From the MDN page about the behaviour of the typeof operator: null // This stands since the beginning of JavaScript typeof null === ‘object’; In the first implementation of JavaScript, JavaScript values were represented as a type tag and a value. The type tag for objects was 0. null was represented as the NULL pointer … Read more
The JVM is caching Integer values. Hence the comparison with == only works for numbers between -128 and 127. Refer: #Immutable_Objects_.2F_Wrapper_Class_Caching
Async prefix is a kind of wrapper for Promises. async function latestTime() { const bl = await web3.eth.getBlock(‘latest’); console.log(bl.timestamp); // Returns a primitive console.log(typeof bl.timestamp.then == ‘function’); //Returns false – not a promise return bl.timestamp; } Is the same as function latestTime() { return new Promise(function(resolve,success){ const bl = web3.eth.getBlock(‘latest’); bl.then(function(result){ console.log(result.timestamp); // Returns a … Read more
Generics in Java are an entirely compile-time construct – the compiler turns all generic uses into casts to the right type. This is to maintain backwards compatibility with previous JVM runtimes. This: List<ClassA> list = new ArrayList<ClassA>(); list.add(new ClassA()); ClassA a = list.get(0); gets turned into (roughly): List list = new ArrayList(); list.add(new ClassA()); ClassA … Read more