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Java Cert - Ch -6
Java.lang Math and String Wrappers
40
Computer Science
Undergraduate 4
02/19/2006

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Cards

Term
what is a string in java?
Definition
in java string is a 16 bit character.
Term
why are strings immutable in jav?
Definition
jvm sets aside a string constants pool. if a similar string is detected
its reference to new string points to old string. saving memory
Term
can some one extendthe string class
Definition
nope that si to ensure the immutability of strings remains intact.
Term
what is the difference between the implicit creation of strings and the explicit creation?
Definition
in implicit creation just one string object is created in the pool . in explicit both an object in the pool and a object not in the pool are created.
Term
what does the first argumetn in substring method represent?
Definition
starting point from where you should substring . This should be a zero based string.
Term
what does the second argument in the substring represent?
Definition
the second arg is the ending point based on 1 based counting
Term
what does the trim method in the string class do.
Definition
the trim method eliminateds any white spaces in the string.
Term
when would you use StringBuffer instead of String class?
Definition
when you will be a lot of modifications on strings so that you dont end up with too many string objects in the pool
Term
what is the difference between String and StringBuffer class.
Definition
the String class is immutable. All created objects are left in a pool. StringBuffer is mutalbe and objects are not left in any pool
Term
what is one syntatical sugar you can use due to mutability of StringBuffer.
Definition
you can say sb.append("xyz").reverse().insert(3,---) it is called method chaining.
Term
what is the output of StringBuffer sb = new StringBuffer("Hello).insert(4,"---");
Definition
Hell---o
Term
why are string methods synchronized.
Definition
because they are all acting on the same data.
Term
how shoulc you read chaining of methods?
Definition
from left to right . output of one method becomes input of the other methods.
Term
how come we dont have to use import statement ot get access to String class?
Definition
all classes in the java.lang package are imported automatically.
Term
can you create object of java.lang.Math
Definition
NO the constructor is private. and you cant extend it the class is final. all methods are static.
Term
what is Math.ceil(-8.9)?
Definition
it is -8.0 !! -8 is greater than -9.
Term
can a ceil method take integers can it return integers.
Definition
NO! ceil method takes doubles and returns doubles.
Term
what is Math.floor(-9.8)?
Definition
-10
Term
what is the result of calling Math.random()?
Definition
a double between 0 and .9999
Term
what does round() do?
Definition
adds .5 and truncates
Term
what does sin() do.
Definition
commits a sin in radians with a double
Term
how to convert 90.0 to radians?
Definition
Math.toRadians(45.0);
Term
what does sqrt(-1) do
Definition
returns NaN.
Term
how do you determine something is positive infinity , neg infinity of nan
Definition
Float.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY,
Double.NaN
Term
How do you check that double is Nan?
Definition
Double.isNaN(a)
Term
what is double devided by 0.0
Definition
it is NaN
Term
What is double devided by -0.0
Definition
it si Doble.NEGATIVE_INFINITY
Term
what happens if you devide integers and floats with 0
Definition
you get arithemetic exception.
Term
Which primitive doesnt have a Wrapper class?
Definition
every primitive has a wrapper class
Term
What are the types of constructors which wrapper classes tend to have?
Definition
two constructors one for their respective types and another to take a string and makeit an integer or whatever
Term
what kind of values will Boolean take.
Definition
case insensitive string or actual boolean
Term
can a boolean object be used in a if statement?
Definition
NO NO NO
Term
what is the significance of the valueOf method()?
Definition
it can take two arguments like
Integer.valueOf("101011",2) that becomes 43. ie radix allowed.
Term
How do you get primitive out of Wrapper?
Definition
(new Integer(42)).shortValue();
Term
What is the difference between parseXxx() and valueOf()?
Definition
both take strings first one returns the primitive second one returns the wrapper.
Term
What is the difference between most methods in Wrappers and the toString() method.
Definition
the toString() method is a non static method.
Term
What is the function of the toXxxString() method.
Definition
can be used to convert string to Binary, Hex or Octal.
Term
what does using == with two reference variables mean?
Definition
it means weather they do point to the same object
Term
when used with wrapper objects how does the equals method behave?
Definition
if both the type of the object and its value are the same ti returns true.
Term
does the StringBuffer class have an equals method.
Definition
NO. it uses Object equas method which i tink compares references dont knwo
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