CIS 120 Lab 3

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CIS 120 Lab 3

• Before we get started...

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• public class Furniture
• private Color c
• public Furniture(Color color)
• c color
• public Furniture() c Color.Red()
• public class Chair
• private int nLegs
• public Chair(Color c, int legs)
• super(c)
• nLegs legs
• public Chair(int legs)nLegs legs

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• gt Item i new Item(null)
• gt i
• null
• gt i null
• false

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Why Extend?
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Midterm 1 Wednesday, Sep 30th (in Class)
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Warm-up Code Comprehension
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public class Arrays int a, b
Arrays(int a, int b) this.a a
this.b b public int arrayDiff()
...
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public int arrayDiff() int diff new
inta.length int i for (i 0 i lt
a.length i) diffi ai - bi
return diff
gt Arrays both, more gt x 1,2,3,4 gt y
5,5,5,5 gt both new Arrays(x, y) gt
both.arrayDiff()
gt z both.arrayDiff() gt more new Arrays(x,
z) gt more.arrayDiff()
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public int arrayDiff() int diff new
inta.length int i for (i 0 i lt
a.length i) diffi ai - bi
return diff
Find an IndexOutOfBoundsException.
What other exception is possible?
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public int arrayDiff() int diff new
inta.length int i for (i 0 i lt
a.length i) diffi ai - bi
return diff

• Fix the method to avoid exceptions.

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Stack and Heap
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• public class Arm
• public int length
• public Arm (int length)
• this.length length

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• public class Torso
• public Arm l, r
• public Torso (Arm l, Arm r)
• this.l l
• this.r r

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gt Arm a new Arm(1) gt Torso t new Torso(a, a)
Draw the stack and the heap.
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• gt Arm a, b
• gt Torso t1, t2
• gt a new Arm(3)
• gt b new Arm(3)
• gt t1 new Torso(a, b)
• gt t2 new Torso(t1.l, t1.r)
• gt t1.r.length 6

Draw the stack and the heap.
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• gt Arm a new Arm(3)
• gt Arm b new Arm(4)
• gt Torso t new Torso(a, b)
• gt a new Arm(3)
• gt b new Arm(a.length)
• gt t new Torso(a, b))

Draw the stack and the heap.
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Inheritance
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public class A int x() return 0 int
y() return 1 public class B extends A
int y() return 2
gt A a new B() gt a.x() gt a.y()
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public class A int x() return 0 int
y() return 1 public class C extends A
int x() return super.x() - 1 int y()
return x() 5
gt A a new C() gt a.x() gt a.y()
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public class C extends A int x() return
super.x() - 1 int y() return x() 5
public class D extends C int x()
return super.x() - 1
gt A a new D() gt a.x() gt a.y()
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Inheritance and Heap Drawings
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public class Counter int count
Counter(int count) this.count count
Counter increment() count
return this String toString()
return at count
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public class Strange extends Counter
Strange(int count) super(count)
Counter increment() return new
Strange(count 1)
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Counter increment() // Counter count
return this Counter increment() // Strange
return new Strange(count 1)
gt Counter a new Counter(0) gt Counter b a gt
a.increment() gt a gt b
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Counter increment() // Counter count
return this Counter increment() // Strange
return new Strange(count 1)
gt Counter a new Counter(0) gt Counter b a gt
a.increment().increment().increment() gt a gt b
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Counter increment() // Counter count
return this Counter increment() // Strange
return new Strange(count 1)
gt Counter a new Strange(0) gt Counter b a gt
a.increment().increment().increment() gt a gt b
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That's all, folks.