Decision and Control Flow

Jython's control flow is standard Python: if/elif/else for decisions, and truthiness rules for conditions. The syntax is identical to CPython, which is the point - you bring your Python knowledge over unchanged.

if / elif / else

score = 85

if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
else:
    grade = "F"

print(grade)  # B

Comparison and Logic

a, b = 5, 10
print(a < b)          # True
print(a == b)         # False
print(a != b)         # True
print(3 < a < 10)     # chained comparison: True

x = 7
if x % 2 == 0 and x > 4:
    print("even and big")
elif x % 2 != 0 or x < 3:
    print("odd or small")  # this branch runs

Truthiness

Empty containers, zero, None, and False are falsy; everything else is truthy - same as Python:

items = []
if not items:
    print("no items")  # runs

msg = ""
print(bool(msg))  # False

Conditional Expressions

age = 20
status = "adult" if age >= 18 else "minor"
print(status)  # adult

Conditions Involving Java Objects

import java.util

lst = java.util.ArrayList()
if lst.isEmpty():          # Java method returning boolean
    print("java list is empty")

s = java.lang.String("")
if len(s) == 0:            # len works on java.lang.String
    print("empty string")

Style Notes

• Indentation defines blocks - keep it consistent (4 spaces).
• No braces or colons-on-next-line: the colon ends the header, the indented block is the body.
• Keep condition expressions simple; extract complex boolean logic into named booleans for readability.

Summary

Control flow in Jython is plain Python: if/elif/else with indented blocks, chained comparisons, and/or/not logic, truthiness for empty values, and the conditional (ternary) expression. Java objects plug into conditions naturally - Java booleans and len()-able strings behave as expected in Python conditionals.