Objects contains data and methods Class – type of object Create class first Then object or instance String – defined class String s; // creates instance.

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Objects contains data and methods Class – type of object Create class first Then object or instance String – defined class String s; // creates instance of string s.length() calls method defined in class Most methods in String return a new string

Examples of objects Scanner console = new Scanner (System.in); File f = new File(“hamlet.txt”); Scanner input = new Scanner (f); Scanner input = new Scanner (new File(“hamlet.txt”)); String s1 = new String (“hello”); Or String s1 = “hello”;

> import java.awt.Point; // auto-import > Point p = new Point(3,8); > System.out.println(p); java.awt.Point[x=3,y=8] > p.translate(-1,-2); > System.out.println(p); java.awt.Point[x=2,y=6]

Reference semantics int x = 3; //primitive type x 3//value semantics Point p = new Point(3,8); //object p  x 3 y 8//reference semantcis P refers to the object When working with objects, always working with reference to data rather than data itself

import java.awt.Point; public class PointExamp1 { public static void main(String[] args) { Point p1 = new Point(3,8); Point p2 = new Point(); Point p3 = p2; System.out.println("p1 = " + p1); System.out.println("p2 = " + p2); System.out.println("p3 = " + p3); p1.x = -1; p1.y = 1; p2.x = -2; p2.y = 2; p3.x = -3; p3.y = 3; System.out.println("p1 = " + p1); System.out.println("p2 = " + p2); System.out.println("p3 = " + p3); } > java PointExamp1 p1 = java.awt.Point[x=3,y=8] p2 = java.awt.Point[x=0,y=0] p3 = java.awt.Point[x=0,y=0] p1 = java.awt.Point[x=-1,y=1] p2 = java.awt.Point[x=-3,y=3] p3 = java.awt.Point[x=-3,y=3]

Multiple objects Point p1 = new Point(3,8); // separate instance Point p2 = new Point(); //separate instance Point p3 = p2; // points to p2

Objects as parameters to Methods public static void manipulate (Point p) { p.x = 99; p.y = 99; } Point p1 = new Point(3,3); manipulate(p1);

import java.awt.Point; public class PointExamp1 { public static void main(String[] args) { Point p1 = new Point(3,8); Point p2 = new Point(5,2); silly(p1); silly(p2); Point p3 = p1; silly(p3); System.out.println("p1 = " + p1); System.out.println("p2 = " + p2); System.out.println("p3 = " + p3); } public static void silly (Point p) { int temp = p.x; p.x = p.y; p.y = temp; }

Evaluate the following What are the x and y coordinates of the Points p1,p2, and p3 after the following? Point p1 = new Point(17,9); Point p2 = new Point(4,-1); Point p3 = p2; p1.translate(3,1); p2x = 50; p3.translate(-4,5)

public class StringComparision1 { public static void main(String[] args) { String name1 = "Bob"; String name2 = new String("Bob"); String name3 = "Bob"; // 1st case if (name1 == name2) { System.out.println("The strings are equal."); } else { System.out.println("The strings are unequal."); } // 2nd case if (name1 == name3) { System.out.println("The strings are equal."); } else { System.out.println("The strings are unequal."); }

public class Temperature { public static void main(String[] args) { double tempf = 98.6; double tempc = 0.0; ftoc(tempf,tempc); System.out.println(“Body temp in C is: “ + tempc); } public static void ftoc(double tempf, double tempc) { tempc = (tempf – 32) * 5/ 9; }

Evaluate the following Math.abs(-1.6) Math.pow(6,2) Math.max(7,4) Math.min(-2,-5) Math.sqrt(64) Math.abs(2 + -4) Math.sqrt(16) * Math.max(Math.abs(- 5),Math.abs(-3))