Lo tienes explicado en http://lineadecodigo.com/java/dibujar-una-figura-con-bucles/
p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Monaco; color: #3f7f5f}
p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Monaco; color: #6a3e3e}
p.p3 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Monaco; min-height: 15.0px}
p.p4 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Monaco}
span.s1 {color: #000000}
span.s2 {text-decoration: underline}
span.s3 {color: #7f0055}
span.s4 {color: #6a3e3e}
span.s5 {color: #0000c0}
span.s6 {color: #2a00ff}
// Declaramos la variables columnas y filas.
int columnas;
int total_filas = 7;
int filas = total_filas; // Tenemos 7 filas.
while (filas > 0) {
columnas = total_filas - filas;
while (columnas > 0) {
System.out.print('*');
columnas--;
}
System.out.println('*');
filas--;
}
filas = 0;
while (filas <= total_filas) {
columnas = total_filas - filas;
while (columnas > 0) {
System.out.print('*');
columnas--;
}
System.out.println('*');
filas++;
}