String Methods.toUpperCase() | .equals(str) | .toLowerCase() | .indexOf(e) | .substring(i,j) j is excluded | .concat(str) | .length() | .charAt(i) | .compareTo(str) | .contains(e) | Integer.parseInteger(intString) | Double.parseDouble(doubleString) |
import java.util.Scanner;
Scanner input= new Scanner(System.in);
Scanner Methods:
.nextLine() ends with line
.next() ends with white space
.nextDouble()
.nextInt() Namingkeywords | lowercase | rule | variables | camelCase | convention | constants | ALL_CAPS | rule | class names | CamelCase | convention |
Math MethodsMath.pow(a, b) | Math.PI() | Math.log(x), Math.log10(x) | Math.sqrt(x) | Math.floor rounds down | Math.ceil() rounds up | Math.random() | Math.min(), Math.max() |
import java.lang.Math;
has sin, cos, tan, toRadians, toDegree, asin, acos, atan
low + Math.random()* high (non-inclusive) Escape Sequences\t | tab | \n | newline | \" | double quote | \\ | backslash |
Date Classjav.util.Date date= new java.util.Date; | date.toString(); |
Point2D Classimport java.geometry.Point2D; | Point2D variable = new Point2D(x, y); |
Objectsno variable constructor | Circle() {
} | constructor | Circle (double radius) {
this.radius=radius;} | getter | double getArea() {
return 2 x radius x radius x Math.PI; } | setter | void setRadius(double radius) {
this.radius=radius;} | instanceof | tests whether an object is an instance of a class | super(); | calls no arg constructor of superclass | super(arg); | calls matching arg constructor of superclass | array of objects | for (int i, i<thing.length, i++)
array[i]= new Thing(param);} |
"this.radius" is an instance variable, as is the original data field
"radius" is the local variable
constructors must have same name as class
constructors do not have a return type, not even void
constructors are invoked using the new operator when an object is created
default constructor goes to class with no other constructors defined | | Abstract Classes and InterfacesAbstract Classes | Interfaces | cannot use "new" | only has abstract methods | methods have no body | no constructors | mix of abstract/non-abstract methods | "implements" | "extends" | contains constants | has constructors | contains contacts and variables |
public abstract class ClassName {
java.lang.Comparable
public interface comparable <E>{
public int compareTo(E o); }
returns -1 for less than, 0 for equals, 1 for greater than
java.lang.Cloneable
public interface clonable {}
use .clone() Loopswhile | int x=n;
while (x>1) {
change x; } | for | for (int i, i<variable, i++){ | for each (arrays) | for (int i: list){ | boolean | (boolean ? true : false) |
Characters.isDigit(ch) | .isLetter(ch) | .isLowerCase(ch), .isUpperCase(ch) | .toLowerCase(ch), .toUppercase(ch) |
ArrayList Methodscreate | ArrayList<type> name = new ArrayList<type>(); | access element | list.get(i) | update element | list.set(i, e) | return size | list.size() | add element | list.add((i), e) | remove element | list.remove(i or e) | remove all elements | list.clear() |
import java.util.ArrayList; Important methodsmodifier returnValueType methodName(params){ | public Class ClassName{
public static void main (String[] args) | Scanner input= new Scanner(System.in) | System.out.println(line); | public static type name (type param){
return type; } | public boolean equals (Object o){
if (o instance Person){
Person p= (Person) o;
return this.name.equals(p.getName()));
}else{
return false;
}
} | public String toString(){
return "String";} |
to use a method from a different class:
Class.method(var); | | Array methodsjava.util.Arrays.sort(array) | .length | java.util.Arrays.equal(a1, a2) | if corresponding elements are the same | Arrays.toString(array) | .reverse() | array[i] | array[i]=e |
import java.util.Arrays;
int[] values= new int[10]
default values: 0, /u0000, or false
printing gives reference
methods can modify arrays
import java.util.Arrays;
multi-dimensional arrays: arrays of arrays.
elementType [rows][columns] arrayVar Vocabularycomposition | information belongs to one object | association/segregation | information can belong to many objects | public visibility | can be seen anywhere in any package | private visibility | can be seen within class | protected visibility | in package and subclasses of this in any package | runtime error | crash | compile error | doesn't run | final static | constant modifier | byte | 8 bits* | block comment | /* ... */ | line comment | // | javadoc comments | /** ... */ | break; | breaks out of a loop | continue; | stays in loop | variable declaration | creating a variable with its type | static | shared by all instances of a class | relational operator | <, <=, ==, !=, >, >= | logical operator | !, &&, || (inclusive), ^ (exclusive) | Numeric Types (in order) | byte, short, int, long, float, double | Variable Scope | variables only exist within {} | assignment operators | =, +=, -=, *=, /=, %= | operators | +, -, %, / (truncates for int) | increment/ decrement operators | ++, -- | instance method | a method that can only be invoked from a specific object | local variable | within a method | instance variable | dependent on the specific instance (class) | overloading methods | methods can have the same name as long as their method signatures are different |
binary operators are left-associative, assignment operators are right associative |
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