Operator Precedence and Operators Example

In this lesson we will discuss about precedence of operators, after that we will see how to read inputs from user and then a small example to show how to operators based on requirements.

Operator Precedence

When we have multiple operations in single expression, then result of that expression depends on weightage of operators in that exression. This is called operator precedence. For example consider an expression 10 + 4 * 3, result might be 42 or 22. Correct answer is 22, because multiplication has higher precedence than addition, hence first 4 * 3 happens then addition operation executes.

Below table shows precedence of operators in decreasing order.

Type Operator Associativity
Postfix () [] . (dot operator) Left to right
Unary ++ – – ! ~ Right to left
Multiplicative * / % Left to right
Additive + – Left to right
Shift >> << Left to right
Relational > >= < <= Left to right
Equality == != Left to right
Bitwise AND & Left to right
Bitwise XOR ^ Left to right
Bitwise OR | Left to right
Logical AND && Left to right
Logical OR || Left to right
Assignment = += -= *= /= %= >>= <<= &= ^= |= Right to left

Reading input from User

Till now all our programs just execute and prints output. They do not accept any input from user. But majority of software applications receive input from user. In this lesson we are going to learn about simple way of taking user input.

Java provides a rich set of libraries of I/O operations. Now we will look at simple library Scanner. This library is present in java.util library. To use scanner class we need to import library into our program. This is achieved by keyword import.

import java.util.Scanner;

Next step we need to do is to create an object or instance of Scanner class. While creating object we need to specify from where it has read inputs that is whether from standard input (console window) or files etc. In our case standard input is sufficient, to do this we need to send System.in has to pass in constructor.

Scanner input = new Scanner(System.in);

To read different types of data Scanner class provides different methods such to read string use input.nextLine() and to read integer input.nextInt() etc. And the return value we can store in a variable.

String name;
name = input.nextLine();

When the above line executing, program waits for user input. On entering input it stores that data into name variable.

Below program demonstrates this method.

/*
This is a simple Java program about User Input.
Call this file KH_UserInput.java.
*/
import java.util.Scanner;

public class KH_UserInput {
	// A Java program begins with a call to main().
	public static void main(String args[]) 
	{
		String name;
		int age;
		
		Scanner input = new Scanner(System.in);
		
		System.out.print("Enter your name: ");
		name = input.nextLine();
		
		System.out.print("Enter your age: ");
		age = input.nextInt();
		
		System.out.println("You name is " + name + " and you are " + age + " old.");
	}
}

Download the code
Run the code

Output:

Enter your name: Khan
Enter your age: 30
You name is Khan and you are 30 old.
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