$ java OverflowBitTrickDemo

=== Hand-rolled overflow detector vs. known cases ===
2000000000 + 2000000000 -> raw int result -294967296, overflow detected: true
2000000000 + -1000000000 -> raw int result 1000000000, overflow detected: false
2147483647 + 1 -> raw int result -2147483648, overflow detected: true
-2147483648 + -1 -> raw int result 2147483647, overflow detected: true
100 + 200 -> raw int result 300, overflow detected: false

=== Cross-checked against Math.addExact() on the same inputs ===
2000000000 + 2000000000: bit-trick says overflow=true, Math.addExact() agrees=true
2000000000 + -1000000000: bit-trick says overflow=false, Math.addExact() agrees=true
2147483647 + 1: bit-trick says overflow=true, Math.addExact() agrees=true
-2147483648 + -1: bit-trick says overflow=true, Math.addExact() agrees=true
100 + 200: bit-trick says overflow=false, Math.addExact() agrees=true