Object methods ¶

XXX#equals ¶

@Override
public boolean equals(Object o) {
    if (o == null) return false; // nothing else to check
    if (this == o) return true; // same
    // check if we can cast
    if (!(o instanceof XXX)) return false;
    // cast
    XXX xxx = (XXX) o;
    // check equals with the attributes
    // ex: xxx.attribute == this.attribute
    return ...;
}

XXX#clone ¶

@Override
public Object clone() {
    XXX xxx;
    try {
        xxx = (XXX) super.clone();
        // you can do some changes here
    } catch (CloneNotSupportedException e) {
        xxx = new XXX(...);
    }
    return xxx;
}

XXX#toString ¶

@Override
public String toString() {
    return "XXX{" +
        "attr1='" + attr1 + '\'' +
        '}';
}

XXX#hashCode ¶

You can use Objects.hashCode(obj), Objects.hash(obj1, obj2...), or obj.hashCode() to get the hashCode of an object (e.g. for attributes...).

@Override
public int hashCode(Object o) {
    // ex: return Objects.hash(attribute1, attribute2);
    return ...;
}

You can calculate a hashCode manually (i.g. not using Objects.hashCode):

@Override
public int hashCode() {
    final int prime = 31; // int max power
    int hash = 1; // return 1
    
    // for each attribute, use the correct line

    // if attr is a boolean
    hash = prime * hash + (attr ? 1231 : 1237);
    // if attr is a char
    hash = prime * hash + attr;
    // if attr is a double
    long doubleTLB = Double.doubleToLongBits(attr);
    hash = prime * hash + (int) (doubleTLB ^ (doubleTLB >>> 32));
    // if attr is a float
    hash = prime * hash + Float.floatToIntBits(attr);
    // if attr is an int
    hash = prime * hash + attr;
    // if attr is an object
    hash = prime * hash + (attr == null ? 0 : attr.hashCode());

    return hash;
}