Override Hashcode and Equals

The correct way to override equals and hashCode methods for Java classes

public class Stock {
    private String symbol;
    private String exchange;
    private long lotSize;
    private int tickSize;
    private boolean isRestricted;
    private Date settlementDate;
    private BigDecimal price;
        
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((exchange == null) ? 0 : exchange.hashCode());
        result = prime * result + (isRestricted ? 1231 : 1237);
        result = prime * result + (int) (lotSize ^ (lotSize >>> 32));
        result = prime * result + ((price == null) ? 0 : price.hashCode());
        result = prime * result + ((settlementDate == null) ? 0 : settlementDate.hashCode());
        result = prime * result + ((symbol == null) ? 0 : symbol.hashCode());
        result = prime * result + tickSize;
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (obj == null || this.getClass() != obj.getClass()){
            return false;
        }
        Stock other = (Stock) obj;
        return
            this.tickSize == other.tickSize &&
            this.lotSize == other.lotSize &&
            this.isRestricted == other.isRestricted &&
            (this.symbol == other.symbol || (this.symbol != null && this.symbol.equals(other.symbol))) &&
            (this.exchange == other.exchange|| (this.exchange != null && this.exchange.equals(other.exchange))) &&
            (this.settlementDate == other.settlementDate|| (this.settlementDate != null && this.settlementDate.equals(other.settlementDate))) &&
            (this.price == other.price|| (this.price != null && this.price.equals(other.price)));
    }
}