Smart Contracts: Programmable Trust

// Familiar Java code that runs on blockchain
public class TokenContract {
    private Map<String, Long> balances = new HashMap<>();
    private long totalSupply;
 
    public TokenContract(long initialSupply) {
        this.totalSupply = initialSupply;
        this.balances.put(getDeployer(), initialSupply);
    }
 
    public boolean transfer(String to, long amount) {
        String from = getCaller();
        if (balances.getOrDefault(from, 0L) < amount) {
            return false;
        }
 
        balances.put(from, balances.get(from) - amount);
        balances.put(to, balances.getOrDefault(to, 0L) + amount);
        return true;
    }
 
    public long getBalance(String address) {
        return balances.getOrDefault(address, 0L);
    }
}

// Security features built into the VM
public class SecureContract {
    // ✅ Network access disabled automatically
    // ✅ File system access prevented
    // ✅ Reflection API removed for determinism
    // ✅ Threading operations disabled
    // ✅ Memory limits enforced (64MB heap)
    // ✅ Stack depth limited (1024 levels)
    // ✅ Call depth limited (64 levels)
 
    public void secureMethod() {
        // All operations are automatically sandboxed
        // No special security annotations needed
    }
}

public class GasOptimizedContract {
    // Gas costs are predictable and fair
    public void efficientLoop(int iterations) {
        for (int i = 0; i < iterations; i++) {
            // Each operation consumes predictable gas
            // No surprise gas spikes
            performOperation(i);
        }
    }
 
    private void performOperation(int value) {
        // Gas metering prevents infinite loops
        // Developers can estimate costs accurately
    }
}

public class PrivateAuction {
    private List<EncryptedBid> bids = new ArrayList<>();
    private long auctionEndTime;
 
    public void submitBid(EncryptedBid encryptedBid) {
        // Bid amount remains encrypted
        // Zero-knowledge proof validates bid without revealing amount
        if (validateBidProof(encryptedBid)) {
            bids.add(encryptedBid);
        }
    }
 
    public EncryptedBid getWinningBid() {
        // Determine winner without revealing any bid amounts
        return findWinnerWithoutDecryption(bids);
    }
}

public class PrivateDEX {
    private Map<String, Map<String, EncryptedAmount>> liquidityPools;
 
    public boolean swapAssets(
        String fromAsset,
        String toAsset,
        EncryptedAmount fromAmount
    ) {
        // Perform atomic swaps with encrypted amounts
        // Maintain privacy while ensuring fair exchange rates
        EncryptedAmount toAmount = calculateSwapAmount(fromAsset, toAsset, fromAmount);
 
        if (validateSwapProof(fromAmount, toAmount)) {
            executePrivateSwap(fromAsset, toAsset, fromAmount, toAmount);
            return true;
        }
        return false;
    }
}

public class PrivateDAO {
    private Map<String, EncryptedVotingPower> votingPowers;
    private List<Proposal> proposals;
 
    public void vote(int proposalId, VoteChoice choice, ZKProof votingProof) {
        // Vote privately while proving eligibility
        // Voting power remains encrypted
        // Results are tallied without revealing individual votes
        if (validateVotingEligibility(votingProof)) {
            recordPrivateVote(proposalId, choice, votingProof);
        }
    }
 
    public ProposalResult tallyVotes(int proposalId) {
        // Count votes without revealing voting patterns
        return countVotesPrivately(proposalId);
    }
}

# Use standard Java development tools
javac -cp rt/lib/rt.jar -target 8 -source 8 MyContract.java
 
# Deploy to TOS Network
tos contract deploy MyContract.class

// Full IDE support with:
// ✅ Syntax highlighting
// ✅ Code completion
// ✅ Error detection
// ✅ Debugging capabilities
// ✅ Unit testing framework
 
@Test
public void testContractFunction() {
    MyContract contract = new MyContract();
    assert contract.getValue() == expectedValue;
}

public class ContractTest {
    @BeforeEach
    void setUp() {
        // Set up test environment
        blockchain = new TOSTestBlockchain();
        contract = blockchain.deploy(MyContract.class);
    }
 
    @Test
    void testTransfer() {
        // Test contract functionality
        boolean result = contract.transfer("alice", 100);
        assertTrue(result);
        assertEquals(100, contract.getBalance("alice"));
    }
}

Memory Limits:
├── Heap Size: 64MB maximum
├── Stack Depth: 1024 levels
├── Call Depth: 64 levels
└── Execution Time: Gas-limited

Storage Efficiency:
├── State Size: Optimized encoding
├── Code Size: Java bytecode compression
└── Total Overhead: Minimal

public class IsolatedContract {
    // Automatic security enforcement:
 
    // ❌ Network operations disabled
    // private void networkCall() { /* Would fail */ }
 
    // ❌ File system access prevented
    // private void fileAccess() { /* Would fail */ }
 
    // ❌ System calls blocked
    // private void systemCall() { /* Would fail */ }
 
    // ✅ Only blockchain operations allowed
    public void blockchainOperation() {
        // Safe operations only
    }
}

public class TimeContract {
    public long getCurrentTime() {
        // Returns deterministic blockchain time
        // Same across all nodes
        return getBlockTimestamp();
    }
 
    public void timeBasedLogic() {
        // All time operations are deterministic
        // No system time dependencies
    }
}

public class GasProtectedContract {
    public void processLargeData(List<String> data) {
        // Gas metering prevents infinite loops
        for (String item : data) {
            processItem(item); // Each iteration costs gas
            // Automatic termination if gas exhausted
        }
    }
}

public class PrivateLendingPool {
    private Map<String, EncryptedAmount> deposits;
    private Map<String, EncryptedLoan> loans;
 
    public boolean deposit(String asset, EncryptedAmount amount, ZKProof proof) {
        if (validateDepositProof(asset, amount, proof)) {
            updateEncryptedBalance(getCaller(), asset, amount);
            return true;
        }
        return false;
    }
 
    public EncryptedLoan requestLoan(
        String collateralAsset,
        EncryptedAmount collateralAmount,
        String loanAsset,
        EncryptedAmount loanAmount,
        ZKProof collateralProof
    ) {
        // Validate collateral without revealing amounts
        if (validateCollateralRatio(collateralAmount, loanAmount, collateralProof)) {
            return issueLoan(loanAsset, loanAmount);
        }
        return null;
    }
}

public class PrivateInsurance {
    private Map<String, EncryptedPolicy> policies;
 
    public void createPolicy(
        String policyholder,
        EncryptedAmount coverage,
        EncryptedAmount premium,
        ZKProof eligibilityProof
    ) {
        if (validateInsurabilityProof(eligibilityProof)) {
            policies.put(policyholder, new EncryptedPolicy(coverage, premium));
        }
    }
 
    public void processClaim(
        String policyholder,
        EncryptedAmount claimAmount,
        ZKProof validClaimProof
    ) {
        // Process claim while maintaining privacy
        if (validateClaimProof(claimAmount, validClaimProof)) {
            payoutClaim(policyholder, claimAmount);
        }
    }
}

# Compile Java contract
javac -cp $TOS_SDK/rt.jar MyContract.java
 
# Deploy to TOS Network
tos contract deploy \
    --contract MyContract.class \
    --network mainnet \
    --gas-limit 1000000 \
    --init-args "arg1,arg2,arg3"

// JavaScript SDK interaction
const contract = await tos.contracts.attach('0x123...contract-address')
 
// Call contract method
const result = await contract.methods.getValue().call()
 
// Send transaction to contract
await contract.methods.setValue(42).send({
    from: userAddress,
    gas: 100000
})

// Upgradeable contract pattern
public class UpgradeableContract {
    private String implementationAddress;
 
    public void upgrade(String newImplementation, ZKProof adminProof) {
        if (validateAdminProof(adminProof)) {
            implementationAddress = newImplementation;
        }
    }
 
    public Object delegateCall(String method, Object[] args) {
        // Delegate to current implementation
        return callImplementation(implementationAddress, method, args);
    }
}

public class PrivacyEnabledContract {
    public void processPrivateTransaction(
        EncryptedAmount amount,
        ZKProof validityProof,
        RangeProof rangeProof
    ) {
        // Verify proofs without seeing amounts
        if (verifyZKProof(validityProof) && verifyRangeProof(rangeProof)) {
            updateEncryptedState(amount);
        }
    }
}

public class AIMiningContract {
    public void validateAIWork(
        String taskId,
        EncryptedSolution solution,
        ZKProof workProof
    ) {
        // Validate AI mining work submissions
        if (validateAIWorkProof(taskId, solution, workProof)) {
            rewardMiner(getCaller(), calculateReward(taskId));
        }
    }
}

public class EnergyEfficientContract {
    public void energyOptimizedOperation() {
        // Use TOS Energy instead of gas fees
        if (hasStakedEnergy(getCaller())) {
            consumeEnergy(getCaller(), getOperationEnergyCost());
            performOperation();
        } else {
            // Fall back to gas fees
            chargeGasFee(getCaller(), getOperationGasCost());
            performOperation();
        }
    }
}