Operators
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Contents
Compound Operators
- +=, -=, *= and /=
- Makes code compact
- Operator precedence for compound assignments : The expression on the right side of the = will always be evaluated first!
int x = 2;
x *= 3 + 5;
//This is equivalent to x = x * (3 + 5) and NOT x = (x*2) + 5.
Relational Operators
- Can be applied to ANY combination of integers, floats or chars.
- int's can be compared to doubles
- char's can be compared to int's
int i = 4;
double pi = 3.14;
if( i > pi) {
System.out.println("Greater than pi");
}
char c = 'C';
if( c > 66) {
System.out.println("C > B");
}
Equality Operators
- '==' and '!=' are used to test for equality.
- Can't compare incompatible types.
- For e.g can't compare an int and a boolean or a Thread and a String
- Objects in the same hierarchy can be checked however.
Object o = new Object();
String s = new String("a");
Integer i = new Integer(42);
if(o == s) { //String IS-A object
System.out.println("o==s");
}
if (s == i) { // Compiler error
}
- For enums, == is equivalent to equals(), because there's no way to create additional enum constants after the declaration.
instanceof
- The instanceof (all small letters) is used for object variables only.
- The first operand must be an object instance and the second operator a class name.
- Instanceof can be used to compare operands which are in the same class hierarchy, However this restriction does not apply to interfaces !
class GrandFather {
}
class Father extends GrandFather {
}
class Son extends Father {
}
public class InOf {
public static void main(String[] args) {
Father f = new Father();
GrandFather gf = new GrandFather();
Son s = new Son();
if (f instanceof GrandFather) { //OK
}
if (f instanceof Son) { //OK
}
if (f instanceof Thread) { //ILLEGAL COMPARE : NOT OK
}
if (f instanceof Runnable) { //OK TO COMPARE
}
}
}
- If a class's superclass implements an interface then the class will pass the instanceof test for the interface
interface Person {
}
class GrandFather implements Person {
}
class Father extends GrandFather {
}
class Son extends Father {
}
public class InOf {
public static void main(String[] args) {
Son s = new Son();
if (s instanceof Person) {
System.out.println("Son is a Person"); //Will print Son is a Person
}
}
}
- IT IS LEGAL to use null reference in an instanceof check. It will always return false.
- Can also be used for arrays
Integer[] ia = new Integer[20];
if(ia instanceof Number[]) {
System.out.println("Integer[] IS-A Number[]"); //Prints this
}
Arithmetic Operators
- +, -, *, /, % are the arithmetic operators.
- *, /, % have a higher precedence than the + and - operators.
String concatenation operator
- '+' is the only "overloaded" operator in java and can be used to concatenate two strings together.
- WATCH OUT : When integers are concatenated with Strings :
- Evaluation runs from left to right
- If both operands are integers, then addition will take place.
- If one operand is a string, concatenation will happen.
System.out.println(1 + 2 + " abc"); // 3 abc
System.out.println(1 + " abc " + 2); // 1 abc 2
System.out.println(1 + 2 + " abc " + 3); // 3 abc 3
System.out.println(1 + 2 + " abc " + 3 + 4); // 3 abc 34
Conditional Operator
- Is a ternary operator (three operands)
- Syntax:
- x = (boolean expression) ? value to assign if bool expr is true : value to assign if bool expr is false.
- value should match with type of x
int c = (new Random().nextInt(10) > 5) ? 1 : 0;
Logical Operator
- Six logical operators - &, |, ^, !, &&, !!
- & , |, ^ are also bitwise operators - they compare variables bit by bit and return a value whose bits have been set according to the comparison made.
int i = 3;
int j = 5;
int k = i & j; //k = 1;
Short Circuit Logical Operators
- Short circuit && evaluates the first operand and if it resolves to false, it skips evaluating the remaining operands because the end result will be false.
- Short circuit || evaluate the first operand and if it is true, it wont evaluate the rest of the expressions because the end result will be true.
public static void main(String[] args) {
if(expr1() && expr2() && expr3()) {
System.out.println("True");
} else {
System.out.println("False");
}
System.out.println("------------------------------");
if(expr1() || expr2() || expr3()) {
System.out.println("True");
} else {
System.out.println("Flase");
}
}
private static boolean expr1() {
System.out.println("expr1");
return false;
}
private static boolean expr2() {
System.out.println("expr2");
return true;
}
private static boolean expr3() {
System.out.println("expr3");
return true;
}
/* OUTPUT :
expr1
False
------------------------------
expr1
expr2
True
/*
Non Short-Circuit Logical Operators
- When & and | are used, they always evaluate all the operands - nothing is skipped.
public class SCircuit {
public static void main(String[] args) {
if(expr1() & expr2() & expr3()) {
System.out.println("True");
} else {
System.out.println("False");
}
System.out.println("------------------------------");
if(expr1() | expr2() | expr3()) {
System.out.println("True");
} else {
System.out.println("False");
}
}
private static boolean expr1() {
System.out.println("expr1");
return false;
}
private static boolean expr2() {
System.out.println("expr2");
return true;
}
private static boolean expr3() {
System.out.println("expr3");
return true;
}
}
/*
OUTPUT:
expr1
expr2
expr3
False
------------------------------
expr1
expr2
expr3
True
*/