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this
, and variable and array initialization
1 // In file initandcleanup/ex1/Account.java 2 3 public class Account { 4 5 // balance: in American pennies 6 private long balance; 7 8 public Account() { 9 balance = 0; 10 } 11 12 //... 13 } 1 // In file initandcleanup/ex1/Example1.java 2 3 public class Example1 { 4 5 public static void main(String[] args) { 6 7 // Create an empty account 8 Account acct = new Account(); 9 } 10 }
public int indexOf(int ch) { //... } public int indexOf(String str) { //... }
public char[] substring(int beginIndex) { //... } public String substring(int beginIndex) { //... }
s.substring(5);
1 // In file initandcleanup/ex2/Account.java 2 3 public class Account { 4 5 // balance: in American pennies 6 private long balance; 7 8 public Account() { 9 balance = 0; 10 } 11 12 public Account(long initDeposit) { 13 balance = initDeposit; 14 } 15 16 //... 17 } 1 // In file initandcleanup/ex2/Example2.java 2 3 public class Example2 { 4 5 public static void main(String[] args) { 6 7 // Create an empty account 8 Account acct1 = new Account(); 9 10 // Create an account with $ 1 Billion 11 Account acct2 = new Account(100000000000L); 12 } 13 }
1 // In file initandcleanup/ex3/Account.java 2 3 public class Account { 4 5 // balance: in American pennies 6 private long balance; 7 8 // No constructor declared 9 10 // amount: in American pennies 11 public boolean okToWithdraw(long amount) { 12 return (amount <= balance); 13 } 14 15 // ... 16 }
1 // In file initandcleanup/ex4/Account.java 2 3 public class Account { 4 5 // balance: in American pennies 6 private long balance; 7 8 public Account() { 9 } 10 11 // amount: in American pennies 12 public boolean okToWithdraw(long amount) { 13 return (amount <= balance); 14 } 15 16 // ... 17 }
this
Referencethis
is a reference to the current object:1 // In file initandcleanup/ex5/Account.java 2 3 public class Account { 4 5 // balance: in American pennies 6 private long balance; 7 8 public Account() { 9 balance = 0; 10 } 11 12 public Account(long balance) { 13 this.balance = balance; 14 } 15 16 // amount: in American pennies 17 public boolean okToWithdraw(long amount) { 18 return (amount <= this.balance); 19 } 20 21 22 //... 23 }
this
Constructor Invocation this()
calls a constructor from
a constructor
this()
from methods
1 // In file initandcleanup/ex6/Account.java 2 3 public class Account { 4 5 // balance: in American pennies 6 private long balance; 7 private long minBal; 8 9 public Account() { 10 this(0, 200000); 11 } 12 13 public Account(long initDeposit) { 14 this(initDeposit, 200000); 15 } 16 17 public Account(long initDeposit, long minBal) { 18 balance = initDeposit; 19 this.minBal = minBal; 20 } 21 22 //... 23 }
1 // In file initandcleanup/ex7/Account.java 2 3 public class Account { 4 5 // balance: in American pennies 6 private long balance; 7 8 // amount: in American pennies 9 public void deposit(long amount) { 10 11 balance += amount; 12 } 13 14 // ... 15 }
1 // In file initandcleanup/ex7/Example7.java 2 3 // THIS WON'T COMPILE 4 public class Example7 { 5 6 public static void main(String[] args) { 7 8 Account acct; 9 // acct = new Account(); 10 acct.deposit(15000); 11 } 12 }
<init>()
method
<init>()
calls another <init>()
1 // In file initandcleanup/ex8/Account.java 2 3 public class Account { 4 5 // balance: in American pennies 6 private long balance = 200; 7 private long minBal = 100; 8 9 { 10 balance = 400; 11 minBal = 200; 12 } 13 14 // initDeposit, minBal: in American pennies 15 public Account(long initDeposit, long minBal) { 16 17 balance = initDeposit; 18 this.minBal = minBal; 19 } 20 21 // ... 22 } 1 // In file initandcleanup/ex8/Example8.java 2 3 public class Example8 { 4 5 public static void main(String[] args) { 6 7 Account acct = new Account(800, 400); 8 } 9 }
<clinit>()
method
class CoffeeCup { private static int cupCount = 355; static { cupCount = PersistentStorage.getLastCupCount(); } //... }
int[] value; int value[];
private int[] value = new int[10]; { for (int i = 0; i < value.length; ++i) { value[i] = i; } }
private int[] value1 = { 0, 1, 2, 3, 4 }; private Integer[] value2 = { new Integer(0), new Integer(1) };
arrayVar.length
gives you the length of the array
finalize()
automatically invoked by garbage collector before
freeing memory
finalize()
to release finite resources
Create a class named Problem1
that has a no-arg constructor that prints out
the message "No-arg constructor invoked!"
. Add a main()
method in
class Problem1
that creates an instance of the Problem1
class.
Create a class named Problem2
that has two constructors: a no-arg
constructor and a constructor that takes a String
as its only input parameter.
Have the no-arg constructor print out the message "No-arg constructor invoked!"
.
Have the other constructor do two things: first, invoke the no-arg constructor
with this()
; second, print out the String
passed in as the
input parameter. Add a main()
method in
class Problem2
that creates an instance of the Problem2
class
using the constructor that takes a String
. To the constructor, pass in the
String
, "String constructor invoked!"
.
Create a Java application named Problem3
that creates an array of
type Problem1
and length five. Then initialize the first three members
of the array with references to three separate instances
of class
Problem1
.
Create a Java application named Problem4
that
has a private static float variable named coefficient
.
Place the coefficient
variable first in the class.
Second in the class, place a main()
method that
prints out the value of coefficient
. Third in the
class, place a static initialization block that sets
coefficient
to 2.0.
Problem5
that creates
a two dimensional array of ints named lincoln
. Initialize
each array element with the sum of its indices. For example,
lincoln[1][2]
should be initialized to 1 + 2
,
or 3
. Print out all the values stored in the
lincoln
array.
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