Java Cheat code for beginners

Basic syntax

• Java code is written in a file with a .java extension
• A Java program must have a main method with the signature public static void main(String[] args).
• A line of code in Java ends with a semicolon ;
• Code blocks are enclosed in curly braces { }

Variables

• Java is a statically-typed language. This means that variables must be declared before they can be used.
• Variables can be declared using the syntax type variableName;, for example: int myNumber;
• Java supports several primitive data types, such as int, double, boolean, and char.
• The String type is a non-primitive data type in Java.
• Variables can be assigned a value using the = operator, for example: myNumber = 42;
• Variables can also be declared and assigned in one line, for example: int myNumber = 42;

Operators

• Java supports various operators, including arithmetic, comparison, and logical operators.
• Arithmetic operators include +, -, *, /, and % (modulus)
• Comparison operators include ==, !=, <, >, <=, and >=
• Logical operators include && (and), || (or), and ! (not)

Control flow

• Java supports various control flow statements, such as if, else, while, for, and switch.
• The if statement is used for conditional execution of code, for example:

if (condition) {
    // code to execute if condition is true
}

• The else statement is used to execute code if the if condition is false, for example:

if (condition) {
    // code to execute if condition is true
} else {
    // code to execute if condition is false
}

• The while loop is used to repeatedly execute code while a condition is true, for example:

while (condition) {
    // code to execute repeatedly while condition is true
}

• The for loop is used to iterate over a range of values, for example:

for (int i = 0; i < 10; i++) {
    // code to execute repeatedly while i is less than 10
}

• The switch statement is used to execute different blocks of code depending on the value of a variable, for example:

switch (variable) {
    case value1:
        // code to execute if variable equals value1
        break;
    case value2:
        // code to execute if variable equals value2
        break;
    default:
        // code to execute if variable does not equal any case value
        break;
}

Classes and objects

• Java is an object-oriented language, which means that code is organized into classes and objects.
• A class is a blueprint for an object. It defines the properties and behaviors that the object will have.
• An object is an instance of a class. It has its own set of properties and can perform its own set of behaviors.
• To create a new object, the new keyword is used, for example: MyClass myObject = new MyClass();
• Properties and behaviors of an object are accessed using the . operator, for example: myObject.myProperty = 42;
• A class can have methods, which are functions that can be called on an object

• Methods can have parameters, which are values passed to the method when it is called, for example:

public void myMethod(int parameter1, String parameter2) { // code to execute with the parameters }

• Methods can also have a return type, which specifies the type of value that the method will return, for example:

public int myMethod() { // code to execute return 42; }

• Constructors are special methods that are called when an object is created. They are used to initialize the properties of the object, for example:

public MyClass(int parameter1, String parameter2) { this.myProperty1 = parameter1; this.myProperty2 = parameter2; }

• The this keyword is used to refer to the current object, for example:
• this.myProperty = 42;

Inheritance and polymorphism

• Inheritance is a mechanism in which a class can inherit properties and behaviors from a parent class.
• A child class is a class that inherits from a parent class, for example:

public class ChildClass extends ParentClass { // child class properties and behaviors }

• Polymorphism is a mechanism in which an object can be treated as an instance of its parent class or as an instance of its own class.
• Overriding is a mechanism in which a child class can override a method from its parent class, for example:

public class ChildClass extends ParentClass { @Override public void myMethod() { // code to execute in the child class } }

Exceptions

• Exceptions are errors that occur during the execution of a program.
• In Java, exceptions are objects that are thrown when an error occurs.
• Exceptions can be caught using try and catch blocks, for example:

try { 
// code that may throw an exception } catch (Exception e) { // code to handle the exception }

• Multiple catch blocks can be used to handle different types of exceptions, for example:

try { 
// code that may throw an exception } catch (IOException e) { // code to handle IOException } catch (NullPointerException e) { // code to handle NullPointerException }

This cheat sheet should give you a good starting point for learning Java programming language. Good luck!