1.3 Expressions and Output

1. Exam Points

• Statements for output
  • System.out.println()
  • System.out.print()
• Escape sequences(转义字符)
  • "
  • \
  • \n
• Arithmetic Operators: +, -, *, /, %
  • int/int is int
  • int/double or double/int is double
  • a/b*c evaluates a/b first, from left to right
  • 13 % 5 is 3
  • divide an integer by zero results in ArithmeticException

2. Knowledge Points

(1) Literals (字面值)

• A literal(字面值) is the code representation of a fixed value.
• A string literal is a sequence of characters enclosed in double quotes.
  • "Annabelle"
  • "0532-89765432"
• Escape sequences(转义字符) are special sequences of characters that can be included in a string.
• They start with a \ and have a special meaning in Java.
• Escape sequences used in this course include:
  • " : displays a "
  • \ : displays a \
  • \n : start a new line
• Example:
  • System.out.println("I "love" sleeping");
  • It prints I "love" sleeping

(2) Arithmetic Expressions(算术表达式)

• Arithmetic expressions, which consist of numeric values, variables, and operators, include expressions of type int and double.
  • Example:
    • a + b
    • a * b / c - d
• Arithmetic operators: +, -, *, /, %
  
• Note:
  • An arithmetic operation on two int values evaluates to an int value.
    • 19/5 is 3
  • An arithmetic operation using at least one double value evaluates to a double value.
    • 13/2.0 is 6.5
    • 15.0/2 is 7.5
  • An attempt to divide an integer by zero will result in ArithmeticException, which is a run-time error.
    • 2/0 leads to error
  • • can be used to concatenate(连接) two String values.
      • "ab"+"cd" is abcd
• Operator Precedence
  • Just like in math, *, /, % first, parentheses first
  • Operators with the same precedence are evaluated from left to right.
    • 5/2*3 is 6, 5/2 is evaluated first
    • 1+2+"a" is 3a
    • "a"+1+2 is a12

3. Exercises

• Practice
• Solution