First Example in Java

Variables

What is a variable?
A piece of memory
Holds data
For example a number, string or Boolean
Java variables have a fixed size
- Platform independence

Java Primitive Types

Primitive type	Size	Min	Max	Wrapper Type
boolean	-	-	-	Boolean
char	16 bits	Unicode 0	Unicode 2^16-1	Character
byte	8 bits	-128	127	Byte
short	16 bits	-2^15	2^15-1	Short
int	32 bits	-2^31	2^31-1	Integer
long	64 bits	-2^63	2^63-1	Long
float	32 bits	IEEE754	IEEE754	Float
double	64 bits	IEEE754	IEEE754	Double
void	-	-	-	Void

Java Primitive Types

Operator Precedence

Equality and Relational Operators

Operator	Java	Sample	meaning
=	==	x == y	x is equal to y
≠	!=	x != y	x is not equal to y
>	>	x > y	x is greater than y
<	<	x < y	x is less than y
≥	>=	x >= y	x is greater than or equal to y
≤	<=	x <= y	x is less than equal y

Associativity

When two operators with the same precedence the expression is evaluated according to its associativity.
x = y = z = 17
- is treated as x = (y = (z = 17))
- since the = operator has right-to-left associativity
72 / 2 / 3
- is treated as (72 / 2) / 3
- since the / operator has left-to-right associativity

A simple program

public class SimpleProgram{
  public static void main(String[] args){
    int a;
    a = 12;
    a += 2;
    int b;
    b = 4;
    b++;
    b = a*b;
    System.out.println(b);
  }
}

Example

A method is like a machine
Zero or more inputs
Zero or one output

Other names
- Function
- Procedure

method

inputs

output

Example

public class Example{
  static double add(double a, double b){
    double result = a + b;
    return result;
  }

  public static void main(String args[]){
    double x = 3;
    double y = 4;
    double add = add(x,y);
    System.out.println(add);
  }
}

Parameter Passing

Local variables
Java passes the parameters by value

public class ParameterPassing{}
  public static void main(String[] args) {
  	double x = 3;
  	double y = 4;
  	double add = add(x,y);
  	System.out.println(add);
  	System.out.println(x);
  }

  static double add(double a, double b){
  	a = a + b;
  	return a;
  }
}

Conditions

public class Main{
  public static void main(String[] args){
    int x = 2;
    int y = 3;

    if(x>y){
    	System.out.println("X is greater than Y");
    } else if(x==y){
    	System.out.println("X is equal to Y");
    } else {
    	System.out.println("Y is greater than X");
    }

    boolean condition = x>y;
    if(condition){
    	System.out.println("X is greater than Y");
    }else{
    	System.out.println("Y >= X");
    }
  }
}

Loops

public class Loop{
  public static void main(String[] args){
    int counter = 0;
    while(counter < 10){
    	counter++;
    	System.out.println(counter);
    }

    counter = 0;
    do{
    	counter++;
    	System.out.println(counter);
    }while(counter < 10);

    for (int i = 1; i <= 10; i++) {
    	System.out.println(i);
    }
  }
}

For Loop vs. While Loop

for (X; Y; Z) {
	body();
}

X;
while(Y){
	body();
	Z;
}

goto

goto is a reserved word in java
But forbidden!

First Example in Java

Outline

First Example

Review

First program in java

First Example

Java Programs

Variables

Variables

Java Primitive Types

Java Primitive Types

Operator Precedence

Equality and Relational Operators

Associativity

A simple program

Example

Example

Parameter Passing

Conditions

Loops

For Loop vs. While Loop

goto

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