Lecture 2: More types, Methods, Conditionals

Mismatched Types

Java verifies that types always match.

Conversion by casting(强制类型转换)

int a = 2; //a = 2
double a = 2; // a = 2.0 (Implicit)

int a = 18.7; //Error
int a = (int)18.7; // a = 18

double a = 2/3; // a = 0.0
double a = (double)2/3

Methods

public static void NAME(){
    STATEMENTS;
}

// To call a method
NAME();

Multiple Parameters

[...] NAME(TYPE NAME, TYPE NAME){
  STATEMENTS;
}
// To call:
NAME(arg1, arg2);

void means "no type"

Return Values

pulic static TYPE NAME(){
  STATEMENTS;
  return EXPRESSION;
}

Variable Scope 变量作用域

Variables live in the block({}) where they are defined (scope).

Method parameters are like defining a new variable in the method.

Methods: Building Blocks

• Big programs are built out of small methods.
• Methods can be individually developed, tested and reused.
• User of method does not need to know how it works.
• In CS, this is called "abstraction".