So my main should look something like

import java.lang.Math;

public class Rawr {

private double x1;

private double x2;

private double x3;

private double x4;

private double y1;

private double y2;

private double y3;

private double y4;

private double shiftX;

private double shiftY;

private double s1;

private double s2;

private double s3;

private double s4;

public Rawr(){

x1 = 0;

x2 = 0;

x3 = 0;

x4 = 0;

y1 = 0;

y2 = 0;

y3 = 0;

y4 = 0;

}

public void setValues(double newX1, double newX2, double newX3, double newX4, double newY1, double newY2, double newY3, double newY4){

x1 = newX1;

x2 = newX2;

x3 = newX3;

x4 = newX4;

y1 = newY1;

y2 = newY2;

y3 = newY3;

y4 = newY4;

}

public void translate(){

x1 = (x1 + shiftX);

x2 = (x2 + shiftX);

x3 = (x3 + shiftX);

x4 = (x4 + shiftX);

y1 = (y1 + shiftY);

y2 = (y2 + shiftY);

y3 = (y3 + shiftY);

y4 = (y4 + shiftY);

}

private void sideLength1to2(){

double s1 = Math.sqrt((x2 - x1)*(x2 - x1) + (y2 - y1) * (y2 - y1));

double s2 = Math.sqrt((x3 - x2)*(x3 - x2) + (y3 - y2) * (y3 - y2));

double s3 = Math.sqrt((x4 - x3)*(x4 - x3) + (y4 - y3) * (y4 - y3));

double s4 = Math.sqrt((x1 - x4)*(x1 - x4) + (y1 - y4) * (y1 - y4));

return;

}

private void perimeter(){

double p = s1 + s2 + s3 + s4;

}

}

Whilst my tester is

public class RawrTester {

public static void main(String[] args){

Rawr testing = new Rawr();

testing.setValues(1,2,1,4,5,2,3,4);

}

}